Hosted by Juha Tompuri
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a.Intro and the Maritime Construction Programme
b.Merivoimat and Maavoimat
c.Artillery and AA Guns
d.Conscription and Cadre vs Militia
e.Suojeluskuntas and Lotta Svard – 1920’s
f.Govt and Politics of the 1920s
g.Ilmavoimat – foundations in the 1920’s
h.Lapua Movement and the Rise of the IKL
i.Rapproachment between the SDP and the SK
j.The Trumvirate – Mannerheim, Rudolph Walden and Vaino Tanner
a.The Ilmavoimat buildup in the 1930’s - aircraft
b.Aircraft factories and aircraft engines
d.Airline industry and air transport reserves
e.Forestry and the military
i. Transportation & mechanization
ii. Ice road techniques and logistics
iii. Firewatching and patrols
iv. Smokejumpers and early ParaJaegers
v. Aircraft for firespotting
viii. Waterbombers, Aerial Refueling, Drop tanks and Molotov Bombs
i. Combat Lights
ii. Nokia Portable Combat Radio
v. The most heavily armed Pigeons in the World
g.The Ilmavoimat again
i. Gyrocopters for the Ilmavoimat
ii. Gyrocopters for the Merivoimat
iii. The “Flour Bomb” project
i. Aarne Somersalo, Architect of the Ilmavoimat’s Air War
ii. Lorentz, Magnusson, Somersalo & doctrinal development
iii. Ilmavoimat volunteers in the Spanish CivilWar
iv. Ilmavoimat Fighter Command and Control System
v. Ilmavoimat Bombing and dive-bombing
vi. AA guns and Air Defence / Antiaircraft gun directors + listening devices
vii. Temporary airfield construction units
i.The Maavoimat in the 1930’s – a Time of Change
i. The Maavoimat in 1930 – a summary
ii. The evolution of Maavoimat doctrine
iii. The evolution of Officer, NCO and Conscript Training – “An Army of Leaders”
iv. The Combined Arms Experimental Unit: flexibility, mobility and the evolution of the Combined Arms Regimental Battle Group
v. Organisational Changes – new units, revised strengths, inclusion of Lottas and Cadets in the mobilized Maavoimat
vi. Mobilization Plan changes
vii. The Spanish Civil War and the Finnish Maavoimat volunteers – lessons learned and applied
viii. The “New” units – Armoured Div, Marines, ParaJaegers, Sissi units, Osasto Nyrkki, “Sea Devils,” special units, Signals Intelligence
ix. The Swiss example and Finland – Rifle Shooting Clubs, a Weapon in every Home, Total War,
x. Propaganda and morale
j.The Finnish Military-Industrial complex: development in the 1930’s
i. The companies
ii. Tampella Tampereen Pellava- ja Rautateollisuus Osake-Yhtiö (Tampere Linen and Iron Industry Ltd., abbreviated to Tampella)
vi. Tikkakoski Rauta ja Puuteollisuusyhtiö
vii. Suojeluskuntain Ase ja Konepaja Oy
viii. VPT - Valtion Patruunatehdas - State Cartridge Factory
ix. VRT - Valtion Ruutitehdas - State Powder Factory
x. VKT - Valtion Kivääritehdas - State Rifle Factory
xi. VTT - Valtion Tykkitehdas - State Artillery Factory
xii. Machine Workshop Leskinen & Kari
xiii. Oy Physica Ab
xiv. Ab Strömberg Oy ..... and more (as has been discussed in the Industrial thread)...
k.Maavoimat weapons design and weapons procurement thru the 1930’s – the Guns
i. The starting point: the Moison-Nagant Rifle
ii. Antti Lahti, Saloranta
iii. First Steps: the Suomi SMG, the 81mm Tampella Mortar and the 76mm Skoda field gun
iv. The SLR Project and the LMG Sampo
v. The 105mm Howitzer
vi. The 120mm Mortar
vii. AA Guns – the 40mm and 76mm Bofors and the first Heavy Artillery Purchase (from France) + artillery tractors
viii. Artillery (US and Brit) + ammunition, Hispano Suiza 20mm AA guns, Anti-tank guns – the 37mm Bofors, the Lahti 20mm
ix. Mines, Rocket Launchers, Flamethrowers,
l. Maavoimat weapons design and weapons procurement thru the 1930’s – the Guns
(this will go into more detail on the artillery pieces and individual purchases, may overlap other headings)
m.Tanks and Vehicles for the Maavoimat
i. Renault FT17’s – the first tanks and armoured units
ii. Second purchase of Renault FT-17’s
iii. 1927/28 and observations on the British Experimental Mechanized Force
(there is a lot more detail planned on this thru the 1930s but I will keeo that as a surprise for noe
i. Nenonen, Master of the Guns
ii. Artillery buildup, guns, units, strength,
iii. Maavoimat Artillery Fire Control System
iv. The Rocket Launchers
o.Fortifying the Isthmus
i. The early fortifications and the geopolitical position
iii. 1936 on – the 4 defence lines and intermediate positions
iv. Coastal Defences (Part 2)
p.Govt and Politics of the 1930’s
q.Foreign Affairs thru the 1920’s and 1930’s and the attempts to build defence treaties
i. Ties with Estonia and Estonian politics, history and the armed forces
iii. Poland & the “secret agreement”
iv. Latvia and Lithuania
v. Ties with the Great Powers - Germany, France, the UK, the USA, Japan
r.The Guns vs Butter debates and Defence Funding through the 1930’s
s.The USSR in the 1930’s - an overview
i. military developments and expansion,
ii. internal and external politics
iii. the Finnish view (including Karelia and Ingria and the Purges)
iv. the Red Army purges
v. Finnish Intelligence
t.The Crucible: The experiences of the Finnish Volunteers in the Spanish Civil War
(this will bring together all the different threads on Finnish involvement in the Spanish Civil War and package them together along with some analysis of what it meant to Finland)
u.“The Great Awakening” – Munich, October 1938
i. The Munich Conference and the abandonment of Czechosolvakia
ii. Mannerheim’s Oct 1938 Speech: “Storm Clouds are gathering over Europe”
iii. Finland takes major steps to improve defence – radical spending
iv. The Emergency Procurement Program of October 1938 (covers emergency purchases from Oct 38 to Nov 39)
v. Dragon’s Teeth - The Isthmus Defence Program accelerated
vi. Trade Links and contingency measures
vii. Applying the lessons of the Spanish Civil War
viii. “Switzerland is our example”
ix. Moving towards a War Economy
v.Alone at the Brink of the Abyss
i. Overtures from the Soviet Union
ii. The Molotov-Ribbentrop Act and the secret protocols
iii. Sept 1939: The Fall of Poland and Polish evacuees to Finland, Franco’s outrage over Poland
iv. The “Maritime Mobilization”
v. Further Pressure from the Soviets – Latvia and Lithuania cave in, Estonia mobilizes, further negotiations
vi. We are not Poland or Czechosolvakia, we are Finns
vii. From Hanko to Petsamo – Finland mobilizes for war
viii. Tensions with Germany & The Last Convoy
ix. The First Volunteers
x. The Opposing Sides
xi. The Evacuation
OK, there's the broad outline up to the actual start of the Winter War. Keep in mind there's as much detail planned under there as there is under the broad headings of what has been completed so far. Months to go (real time) before the fighting starts....
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As a sea-faring nation, Japan had an early interest in wireless (radio) communications. The first known use of wireless telegraphy in warfare at sea was in fact by the Imperial Japanese Navy, in defeating the Russian Imperial Fleet in 1904. There was also an early interest in equipment for radio direction-finding, for use in both navigation and military surveillance. The Imperial Navy developed an excellent receiver for this purpose in 1921, and soon most of the Japanese warships had this equipment. In the two decades between the World Wars, radio technology in Japan made advancements on a par with that in the western nations. There were often impediments, however, in transferring these advancements into the military. For a long time, the Japanese believed they had the best fighting capability of any military force in the world. The military leaders, who were then also in control of the government, sincerely felt that the weapons, aircraft, and ships that they had built were fully sufficient and, with these as they were, the Japanese Army and Navy were invincible.
Radio engineering was strong in Japan’s higher education institutions, especially the Imperial (government-financed) universities. This included undergraduate and graduate study, as well as academic research in this field. Special relationships were established with foreign universities and institutes, particularly in Germany, with Japanese teachers and researchers often going overseas for advanced study. The academic research that was carried out tended toward the improvement of basic technologies, rather than their specific applications. There was considerable research in high-frequency and high-power oscillators, such as the magnetron, but the application of these devices was generally left to industrial and military researchers. One of Japan’s best-known radio researchers in the 1920s-30s era was Professor Hidetsugu Yagi (January 28, 1886 - January 19, 1976, born in Osaka City). After graduate study in Germany, England, and America, Yagi joined Tohoku University where his research centered on antennas and oscillators for high-frequency communications. A summary of the radio research work at Tohoku University was contained in a seminal paper by Yagi published in 1928.
Jointly with Shintaro Uda, one Yagi’s first doctoral students, a radically new antenna emerged. It had a number of parasitic elements (directors and reflectors) and would come to be known as the Yagi-Uda or Yagi antenna, which was patented in Japan in 1926. A U.S. patent, issued in May 1932, was assigned to RCA. To this day, this is the most widely used directional antenna worldwide (it is now installed on millions of houses throughout the world for radio and television reception). The cavity magnetron was also of interest to Yagi. This HF (~10-MHz) device had been invented in 1921 by Albert W. Hull at General Electric, and Yagi was convinced that it could function in the VHF or even the UHF region. In 1927, Kinjiro Okabe, another of Yagi’s early doctoral students, developed a split-anode device that ultimately generated oscillations at wavelengths down to about 12 cm (2.5 GHz). Researchers at other Japanese universities and institutions also started projects in magnetron development, leading to improvements in the split-anode device.
Shigeru Nakajima at Japan Radio Company (JRC) saw a commercial potential of these devices and began the further development and subsequent very profitable production of magnetrons for the medical dielectric heating (diathermy) market. The only military interest in magnetrons was shown by Yoji Ito at the Naval Technical Research Institute (NTRI). The NTRI was formed in 1922, and became fully operational in 1930. Located at Meguro, Tokyo, near the Tokyo Institute of Technology, first-rate scientists, engineers, and technicians were engaged in activities ranging from designing giant submarines to building new radio tubes. Included were all of the precursors of radar, but this did not mean that the heads of the Imperial Navy accepted these accomplishments. In 1936, Tsuneo Ito (no relationship to Yoji Ito) developed an 8-split-anode magnetron that produced about 10 W at 10 cm (3 GHz). Based on its appearance, it was named Tachibana (or Mandarin, an orange citrus fruit). Tsuneo Ito also joined the NTRI and continued his research on magnetrons in association with Yoji Ito. In 1937, they developed the technique of coupling adjacent segments (called push-pull), resulting in frequency stability, an extremely important magnetron breakthrough.
By early 1939, NTRI/JRC had jointly developed a 10-cm (3-GHz), stable-frequency Mandarin-type magnetron (No. M3) that, with water cooling, could produce 500-W power. In the same time period, magnetrons were built with 10 and 12 cavities operating as low as 0.7 cm (40 GHz). The configuration of the M3 magnetron was essentially the same as that used later in the magnetron developed by Boot and Randall at Birmingham University in early 1940, including the improvement of strapped cavities. Unlike the high-power magnetron in Great Britain, however, the initial device from the NTRI generated only a few hundred watts. In general, there was no lack of scientific and engineering capabilities in Japan; their warships and aircraft clearly showed high levels of technical competency. They were ahead of Great Britain in the development of magnetrons, and their Yagi antenna was the world standard for VHF systems. It was simply that the top military leaders failed to recognize how the application of radio in detection and ranging – what was often called the Radio Range Finder (RRF) – could be of value, particularly in any offensive role; offense not defense, totally dominated their thinking.
Japanese Imperial Army:
In 1938, engineers from the Research Office of Nippon Electric Company (NEC) were making coverage tests on high-frequency transmitters when rapid fading of the signal was observed. This occurred whenever an aircraft passed over the line between the transmitter and receiving meter. Masatsugu Kobayashi, the Manager of NEC’s Tube Department, recognized that this was due to the beat-frequency interference of the direct signal and the Doppler-shifted signal reflected from the aircraft. Kobayashi suggested to the Army Science Research Institute that this phenomenon might be used as an aircraft warning method. Although the Army had rejected earlier proposals for using radio-detection techniques, this one had appeal because it was based on an easily understandable method and would require little developmental cost and risk to prove its military value. NEC assigned Kinji Satake of their Research Institute to develop a system called the Bi-static Doppler Interference Detector (BDID).
For testing the prototype system, it was set up on an area recently occupied by Japan along the coast of China. The system operated between 4.0-7.5 MHz (75–40 m) and involved a number of widely spaced stations; this formed a radio screen that could detect the presence (but nothing more) of an aircraft at distances up to 500 km (310 mi). The BDID was the Imperial Army’s first deployed radio-based detection system and was placed into operation in early 1941. A similar system was developed by Satake for the Japanese homeland. Information centers received oral warnings from the operators at BDID stations, usually spaced between 65 and 240 km (40 and 150 mi). To reduce homing vulnerability – a great fear of the military – the transmitters operated with only a few watts power. Although originally intended to be temporary until better systems were available, they remained in operation throughout the war. It was not until after the start of war the Imperial Army had equipment that could be called radar.
WW2 Japanese “Mobile Mattress Radar The Radar operates at 200 mcs. and is identified by a small screen (14′ x 7′) mounted on a Japanese standard army trailer (type 94). This Radar is being used more and more for land-based search, either alone or in conjunction with older types. It is frequently seen mounted in emplacements, suggestive of a permanent siting. Above are reconstructed drawings made from photos of the Kwajalein set. The shack, antennae, revolving mount and trailer may be separated for shipping purposes.
The Mobile Mattress captured at Namur, Kwajalein, was mounted atop the standard concrete power house. Although the set is badly damaged, it is still possible to establish the important recognition features. Several additional views of the “Mobile Mattress” or Mark I, Model 2 are shown for familiarization. This set is very probably the best Japanese Search Radar in general use at present. The frequency is 200 megacycles per second and the maximum range is 100 nautical miles.
More photos of captured Japanese Radars
And lastly, Japanese Radar control boxes
Japanese Imperial Navy
In the mid-1930s, some of the technical specialists in the Imperial Navy became interested in the possibility of using radio to detect aircraft. For consultation, they turned to Professor Yagi who, then the Director of the Radio Research Laboratory at Osaka Imperial University. Yagi suggested that this might be done by examining the Doppler frequency-shift in a reflected signal. Funding was provided to the Osaka Laboratory for experimental investigation of this technique. Kinjiro Okabe, the inventor of the split-anode magnetron and who had followed Yagi to Osaka, led the effort. Theoretical analyses indicated that the reflections would be greater if the wavelength was approximately the same as the size of aircraft structures. Thus, a VHF transmitter and receiver with Yagi antennas separated some distance were used for the experiment.
In 1936, Okabe successfully detected a passing aircraft by the Doppler-interference method; this was the first recorded demonstration in Japan of aircraft detection by radio. With this success, Okabe’s research interest switched from magnetrons to VHF equipment for target detection. This, however, did not lead to any significant funding. The top levels of the Imperial Navy believed that any advantage of using radio for this purpose were greatly outweighed by enemy intercept and disclosure of the sender’s presence. Historically, warships in formation used lights and horns to avoid collision at night or when in fog. Newer techniques of VHF radio communications and direction-finding might also be used, but all of these methods were highly vulnerable to enemy interception. At the NTRI, Yoji Ito proposed that the UHF signal from a magnetron might be used to generate a very narrow beam that would have a greatly reduced chance of enemy detection.
Development of microwave system for collision avoidance started in 1939, when funding was provided by the Imperial Navy to JRC for preliminary experiments. In a cooperative effort involving Yoji Ito of the NTRI and Shigeru Nakajima of JRC, an apparatus using a 3-cm (10-GHz) magnetron with frequency modulation was designed and built. The equipment was used in an attempt to detect reflections from tall structures a few kilometers away. This experiment gave poor results, attributed to the very low power from the magnetron. The initial magnetron was replaced by one operating at 16 cm (1.9 GHz) and with considerably higher power. The results were then much better, and in October 1940, the equipment obtained clear echoes from a ship in Tokyo Bay at a distance of about 10 km (6.2 mi). There was still no commitment by top Japanese naval officials for using this technology aboard warships. Nothing more was done at this time, and it was not until 1941 that the system was adopted for limited use.
Yukikaze (Japanese Destroyer, launched 1940): View of the ship's forward superstructure, taken at Tokyo, Japan, on 26 May 1947. She was then ready for display to representatives of the principal Allied powers and had previously been employed repatriating Japanese nationals from overseas. She later became the Republic of China Navy's destroyer Tan Yang. Note the horn-shaped radar antennas on Yukikaze's foremast (the long pipe running from her forecastle to the port side of her forward smokestack is the galley smoke pipe).
Again, we can see clearly in retrospect that while Japan had world-leading scientists such as Professor Hidetsugu Yagi and were clearly capable of designing and bukding first-class radar systems, Japan’s top military leaders and theorists failed to recognize in time how the application of “radar” could be of value, particularly in any offensive role as offense not defense, totally dominated their thinking.
In 1895, Alexander Stepanovich Popov, a physics instructor at the Imperial Russian Navy school in Kronstadt, developed an apparatus using a coherer tube for detecting distant lightning strikes. The next year, he added a spark-gap transmitter and demonstrated the first radio communication set in Russia. During 1897, while testing this in communicating between two ships in the Baltic Sea, he took note of an interference beat caused by the passage of a third vessel. In his report, Popov wrote that this phenomenon might be used for detecting objects, but he did nothing more with this observation. The years following the 1917 Russian Revolution and the establishment the Union of Soviet Socialist Republics (USSR or Soviet Union) in 1924, Germany’s Luftwaffe had aircraft capable of penetrating deep into Soviet territory. Thus, the detection of aircraft at night or above clouds was of great interest to the Voiska Protivo-vozdushnoi aborony (PVO, Air Defense Forces) of the Raboche-Krest'yanskaya Krasnaya Armiya (RKKA, Workers’–Peasants’ Red Army).
The PVO depended on optical devices for locating targets, and had physicist Pavel K. Oshchepkov (June 24, 1908 - December 1, 1992) conducting research in possible improvement of these devices. In June 1933, Oshchepkov changed his research from optics to radio techniques and started the development of a razvedyvlatl’naya elektromagnitnaya stantsiya (reconnaissance electromagnetic station). In a short time, Oshchepkov was made responsible for a PVO experino-tekknicheskii sektor (technical expertise sector) devoted to radiolokatory (radio-location) techniques as well as heading a Special Construction Bureau (SCB) in Leningrad (formerly St. Petersberg).
The Glavnoe artilkeriisko upravlenie (GAU, Main Artillery Administration) was considered the “brains” of the Red Army. It not only had competent engineers and physicists on its central staff, but also had a number of scientific research institutes. Thus, the GAU was also assigned the aircraft detection problem, and Lt. Gen. M. M. Lobanov was placed in charge. After examining existing optical and acoustical equipment, Lobanov also turned to radio-location techniques. For this he approached the Tsentral’naya radiolaboratoriya (TsRL, Central Radio Laboratory) in Leningrad. Here, Yu. K. Korovin was conducting research on VHF communications, and had built a 50 cm (600 MHz), 0.2 W transmitter using a Barkhausen-Kurz tube. For testing the concept, Korovin arranged the transmitting and receiving antennas along the flight path of an aircraft. On January 3, 1934, a Doppler signal was received by reflections from the aircraft at some 600 m range and 100–150 m altitude.
For further research in detection methods, a major conference on this subject was arranged for the PVO by the Rossiiskaya Akademiya Nauk (RAN, Russian Academy of Sciences). The conference was held in Leningrad in mid-January, 1934, and chaired by Abram Fedorovich Ioffe, Director of the Leningrad Physical-Technical Institute (LPTI). Ioffe was generally considered the top Russian physicist of his time. All types of detection techniques were discussed, but radio-location received the greatest attention. To distribute the conference findings to a wider audience, the proceedings were published the following month in a journal. This included all of the then-existing information on radio-location in the USSR, available (in Russian language) to researchers in this field throughout the world. Recognizing the potential value of radio-location to the military, the GAU made a separate agreement with the Leningrad Electro-Physics Institute (LEPI), for a radio-location system. This technical effort was led by B. K. Shembel. The LEPI had built a transmitter and receiver to study the radio-reflection characteristics of various materials and targets. Shemlbel readily made this into an experimental bi-static radio-location system called Bistro (Rapid).
The Bistro transmitter, operating at 4.7 m (64 MHz), produced near 200 W and was frequency-modulated by a 1 kHz tone. A fixed transmitting antenna gave a broad coverage of what was called a radiozkzn (radio screen). A regenerative receiver, located some distance from the transmitter, had a dipole antenna mounted on a hand-driven reciprocating mechanism. An aircraft passing into the screened zone would reflect the radiation, and the receiver would detect the Doppler-interference beat between the transmitted and reflected signals. Bistro was first tested during the summer of 1934. With the receiver up to 11 km away from the transmitter, the set could only detect an aircraft entering a screen at about 3 km (1.9 mi) range and a under 1,000 m. With improvements, it was believed to have a potential range of 75 km, and five sets were ordered in October for field trials. Bistro is often cited as the USSR’s first radar system; however, it was incapable of directly measuring range and thus could not be so classified. LEPI and TsRL were both made a part of Nauchno-issledovatel institut-9 (NII-9, Scientific Research Institute #9), a new GAU organization opened in Leningrad in 1935. Mikhail A. Bonch-Bruyevich, a renowned radio physicist previously with TsRL and the University of Leningrad, was named the NII-9 Scientific Director.
Research on magnetrons began at Kharkov University in Ukraine during the mid-1920s. Before the end of the decade this had resulted in publications with worldwide distribution, such as the German journal Annalen der Physik (Annals of Physics). Based on this work, Ioffe recommended that a portion of the LEPI be transferred to the city of Kharkov, resulting in the Ukrainian Institute of Physics and Technology (LIPT) being formed in 1930. Within the LIPT, the Laboratory of Electromagnetic Oscillations (LEMO), headed by Abram A. Slutskin, continued with magnetron development. Led by Aleksandr S. Usikov, a number of advanced segmented-anode magnetrons evolved. (It is noted that these and other early magnetrons developed in the USSR suffered from frequency instability, a problem in their use in Soviet radar systems.) In 1936, one of Usikov’s magnetrons producing about 7 W at 18 cm (1.7 GHz) was used by Shembel at the NII-9 as a transmitter in a radioiskatel (radio-seeker) called Burya (Storm). Operating similarly to Bistro, the range of detection was about 10 km, and provided azimuth and elevation coordinates estimated to within 4 degrees. No attempts were made to make this intro a pulsed system, thus, it could not provide range and was not qualified to be classified as a radar. It was, however, the first microwave radio-detection system.
While work by Shembel and Bonch-Bruyevich on continuous-wave systems was taking place at NII-9, Oshehepkov at the SCB and V. V. Tsimbalin of Ioffe’s LPTI were pursuing a pulsed system. In 1936, they built a radio-location set operating at 4 m (75 MHz) with a peak-power of about 500 W and a 10-μs pulse duration. Before the end of the year, tests using separated transmitting and receiving sites resulted in an aircraft being detected at 7 km. In April 1937, with the peak-pulse power increased to 1 kW and the antenna separation also increased, test showed a detection range of near 17 km at a height of 1.5 km. Although a pulsed system, it was not capable of directly providing range – the technique of using pulses for determining range had not yet been developed.
In June 1937, all of the work in Leningrad on radio-location suddenly stopped. The infamous Great Purge swept over the military high command and the supporting scientific community. The PVO chief was executed. Oshchepkov, charged with “high crime,” was sentenced to 10 years at a Gulag penal labor camp. NII-9 as an organization was saved, but Shenbel was dismissed and Bonch-Bruyevich was named the new director. The Nauchnoissledovatel skii ispytalel nyi institut suyazi RKKA (NIIIS-KA, Scientific Research Institute of Signals of the Red Army), had initially opposed research in radio-location, favoring instead acoustical techniques. However, this portion of the Red Army gained power as a result of the Great Purge, and did an about face, pressing hard for speedy development of radio-location systems. They took over Oshchepkov’s laboratory and were made responsible for all existing and future agreements for research and factory production. Writing later about the Purge and subsequent effects, General Lobanov commented that it led to the development being placed under a single organization, and the rapid reorganization of the work to accomplish needed results.
At Oshchepkov’s former laboratory, work with the 4 m (75 MHz) pulsed-transmission system was continued by A. I. Shestako. Through pulsing, the transmitter produced a peak power of 1 kW, the highest level thus far generated. In July 1938, a fixed-position, bi-static experimental system detected an aircraft at about 30 km range at heights of 500 m, and at 95 km range, for high-flying targets at 7.5 km altitude. The system was still incapable of directly determining the range. The project was then taken up by Ioffe’s LPTI, resulting in the development of a mobile system designated Redut (Redoubt). An arrangement of new transmitter tubes was used, giving near 50 kW peak-power with a 10 μs pulse-duration. Yagi antennas were adopted for both transmitting and receiving. The Redut was first field tested in October 1939, at a site near Sevastopol, a port in Ukraine on the coast of the Black Sea. This testing was in part to show the NKKF (Soviet Navy) the value of early-warning radio-location for protecting strategic ports. With the equipment on a cliff about 160 meters above sea level, a flying boat was detected at ranges up to 150 km. The Yagi antennas were spaced about 1,000 meters; thus, close coordination was required to aim them in synchronization.
First experimental Soviet radar – late 1930’s
At the NII-9 under Bonch-Bruyevich, scientists developed two types of very advanced microwave generators. In 1938, a linear-beam, velocity-modulated vacuum tube (a klystron) was developed by Nikolay Devyatkov, based on designs from Kharkov. This device produced about 25 W at 15–18 cm (2.0–1.7 GHz) and was later used in experimental systems. Devyatkov followed this with a simpler, single-resonator device (a reflex klystron). At this same time, D. E. Malyarov and N. F. Alekseyev were building a series of magnetrons, also based on designs from Kharkov; the best of these produced 300 W at 9 cm (3 GHz). Also at NII-9, D. S. Stogov was placed in charge of the improvements to the Bistro system. Redesignated as Reven (Rhubarb), it was tested in August 1938, but was only marginally better than the predecessor. With additional minor operational improvements, it was made into a mobile system called Radio Ulavlivatel Samoletov (RUS, Radio Catcher of Aircraft), soon designated as RUS-1. This continuous-wave, bi-static system had a truck-mounted transmitter operating at 4.7 m (64 MHz) and two truck-mounted receivers.
Soviet Mobile Radar – RUS-1 – 1939. The RUS-1 was used experimentally in the Soviet-Finnish Winter War. At the beginning of the Great Patriotic War the Red Army had about 45 of these radars in service, mostly enrolled in the South Caucasus and the Far East. The introduction of the RUS-1 (and later, the RUS-2) Radar increased the effectiveness of Soviet Air Defence according to Soviet sources. Data on air targets (distance, azimuth, speed flight group and individual goal) from several radars enable air defense command command to evaluate the real situation and effectively use its own resources. On the other hand, Ilmavoimat records indicate that Soviet Air Defence effectiveness was poor and seemed uncoordinated at the best of times. Finnish Signals Intelligence had indentified Soviet radar emissions even before the Winter War had started and attacking Soviet Radar Transmitter Sites was a priority for the Ilmavoimat, although the effectiveness of these attacks on weakening Soviet Air Defence was never really satisfactorally established as the air defence seemed so poor regardless.
Although the RUS-1 transmitter was in a cabin on the rear of a truck, the antenna had to be strung between external poles anchored to the ground. A second truck carrying the electrical generator and other equipment was backed against the transmitter truck. Two receivers were used, each in a truck-mounted cabin with a dipole antenna on a rotatable pole extended overhead. In use, the receiver trucks were placed about 40 km apart; thus, with two positions, it would be possible to make a rough estimate of the range by triangulation on a map. The RUS-1 system was tested and put into production in 1939, then entered service in 1940, becoming the first deployed radio-location system in the Red Army. A total of about 45 RUS-1 systems were built at the Svetlana Factory in Leningrad before the end of 1941, and deployed along the western USSR borders and in the Far East. Without direct ranging capability, however, the military found the RUS-1 to be of little value.
Another Soviet mobile Radar System – RUS-2 – 1940: The RUS-2 Rard was also battle-tested by the Soviets during the Winter War. The RUS-2 was able to detect air targets at up to 120 km. Soviet Air Defence adopted the RUS-2 in June 1940 (06/1940). Hpwever, without direct ranging capability, the military found the RUS-1 to be of little value.
Rear view of a RUS-2 Radar System, photographed by a Maavoimat Osasto Nyrkki team operating behind Red Army Lines during the Winter War – Summer 1940.
Side view of a RUS-2 Radar System. A number of these Soviet Radar Systems were captured by Finnish forces over the course of the Winter War. Reverse engineering however, proved them far inferior to the Finnish-design and built Nokia Radar Systems. Two RUS-2 Radar Systems (together with a range of other captured Soviet military equipment) were also traded to Germany in mid-1940 in return for German agreement to the Finnish purchase of military equipment (via Swedish companies set up for this purpose).
Side view of a Soviet RUS-2 Radar System
Even before the demise of efforts in Leningrad, the NIIIS-KA had contracted with the UIPT in Kharkov to investigate a pulsed radio-location system for anti-aircraft applications. This led the LEMO, in March 1937, to start an internally funded project with the code name Zenit (a popular football team at the time). The transmitter development was led by Usikov, supplier of the magnetron used earlier in the Burya. For the Zenit, Usikov used a 60 cm (500 MHz) magnetron pulsed at 10–20 μs duration and providing 3 kW pulsed power, later increased to near 10 kW. Semion Braude led the development of a superheterodyne receiver using a tunable magnetron as the local oscillator. The system had separate transmitting and receiving antennas set about 65 m apart, built with dipoles backed by 3-meter parabolic reflectors. Zenit was first tested in October 1938. In this, a medium-sized bomber was detected at a range of 3 km. The testing was observed by the NIIIS-KA and found to be sufficient for starting a contracted effort. An agreement was made in May 1939, specifying the required performance and calling for the system to be ready for production by 1941. The transmitter was increased in power, the antennas had selsens added to allow them to track, and the receiver sensitivity was improved by using an RCA 955 acorn triode as the local oscillator.
A demonstration of the improved Zenit was given in September 1940. In this, it was shown that the range, altitude, and azimuth of an aircraft flying at heights between 4,000 and 7,000 meters could be determined at up to 25 km distance. The time required for these measurements, however, was about 38 seconds, far too long for use by anti-aircraft batteries. Also, with the antennas aimed at a low angle, there was a dead zone of some distance caused by interference from ground-level reflections. While this performance was not satisfactory for immediate gun-laying applications, it was the first full three-coordinate radio-location system in the Soviet Union and showed the way for future systems. Work at the LEMO continued on Zenit, particularly in converting it into a single-antenna system designated Rubin. This effort, however, was disrupted by the invasion of the USSR by Germany in June 1941. In a short while, the development activities at Kharkov were ordered to be evacuated into the Far East. The research efforts in Leningrad were similarly dispersed.
After eight years of effort by highly qualified physicists and engineers, the USSR entered World War II without a fully developed and fielded radar system.
Next: Radar development in Germany, Britain and the USA
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In 1930, both the Navy and the Army initiated the development of radio equipment that could be used to remotely locate enemy ships and aircraft. At a high level, the development of radar in the USA from its origins to the end of the war can be viewed in two stages. It was born in the USA in the Naval Research Laboratory from observations made in June 1930 by Leo Young and Laurence Pat Hyland which eventually led in 1934 to Robert Page's building of a 60 MHz pulse radar set. A development of this, the CXAM, became available in November 1939. Twenty sets were installed on battleships, aircraft carriers, and cruisers in 1940.
Within the Army, Major William Blair, the director of the Signal Corps Laboratories at Fort Monmouth, New Jersey, promoted radar experiments from 1933 onwards. A simple pulse radar was demonstrated in December 1936. By May 1937, a prototype of the first US Army radar, the SCR-268, was built. A long-range radar, operating at 106 MHz, the mobile SCR 270 and its fixed counterpart the SCR-271, went into service in 1940. About 800 were produced between 1939 and 1944. By early 1942 the Aircraft Warning Service had a chain of SCR-270 and SCR-271 radars protecting the east coast from Maine to Key West and the west coast from Washington to San Diego. By late 1939, the USA possessed a very solid and developing radar programme though it lacked, perhaps, the urgency engendered by a country threatened by war.
There was little coordination of these efforts; thus, they will be described in detail separately.
United States Navy
In the autumn of 1922, Albert H. Taylor and Leo C. Young of the U.S. Naval Aircraft Radio Laboratory were conducting communication experiments when they noticed that a wooden ship in the Potomac River was interfering with their signals; in effect, they had accidentally demonstrated the first multistatic radar, a system that uses separate transmitting and receiving antennas and detects targets due to changes in the signal. In 1930, Lawrence A. Hyland working with Taylor and Young, now at the U.S. Naval Research Laboratory (NRL) in Washington, D.C., used a similar arrangement of radio equipment to detect a passing aircraft. This led to a proposal by Taylor for using this technique for detecting ships and aircraft.
A simple wave-interference apparatus can detect the presence of an object, but it cannot determine its location or velocity. That had to await the invention of pulsed radar, and later, additional encoding techniques to extract this information from a CW signal. When Taylor's group at the NRL were unsuccessful in getting interference radio accepted as a detection means, Young suggested trying pulsing techniques. This would also allow the direct determination of range to the target. The British and the American research groups were each independently aware of the advantages of such an approach, but the problem was to develop the timing equipment to make it feasible. Robert Morris Page was assigned by Taylor to implement Young's suggestion. Page designed a transmitter operating at 60 MHz and pulsed 10 μs in duration and 90 μs between pulses. In December 1934, the apparatus was used to detect a plane at a distance of one mile (1.6 km) flying up and down the Potomac. Although the detection range was small and the indications on the oscilloscope monitor were almost indistinct, it demonstrated the basic concept of a pulsed radar system. Based on this, Page, Taylor, and Young are usually credited with building and demonstrating the world’s first true radar.
An important subsequent development by Page was the duplexer, a device that allowed the transmitter and receiver to use the same antenna without over-whelming or destroying the sensitive receiver circuitry. This also solved the problem associated with synchronization of separate transmitter and receiver antennas which is critical to accurate position determination of long-range targets. The experiments with pulsed radar were continued, primarily in improving the receiver for handling the short pulses. In June 1936, the NRL's first prototype radar system, now operating at 28.6 MHz, was demonstrated to government officials, successfully tracking an aircraft at distances up to 25 miles (40 km). Their radar was based on low frequency signals, at least by today's standards, and thus required large antennas, making it impractical for ship or aircraft mounting. Antenna size is inversely proportional to the operating frequency; therefore, the operating frequency of the system was increased to 200 MHz, allowing much smaller antennas. The frequency of 200 MHz was the highest possible with existing transmitter tubes and other components.
Radar equipment on the USS Leary, April 1937
The new system was successfully tested at the NRL in April 1937, That same month, the first sea-borne testing was conducted. The equipment was temporarily installed on the USS Leary, with a Yagi antenna mounted on a gun barrel for sweeping the field of view. Based on the success of the sea trials, the NRL further improved the system. Page developed the ring oscillator, allowing multiple output tubes and increasing the pulse-power to 15 kW in 5-µs pulses. A 20-by-23-foot (7.0 m), stacked-dipole “bedspring” antenna was used. In laboratory test during 1938, the system, now designated XAF, detected planes at ranges up to 100 miles (160 km). It was installed on the battleship USS New York for sea trials starting in January 1939, and became the first operational radio detection and ranging set in the U.S. fleet. In May 1939, a contract was awarded to RCA for production. Designated CXAM, deliveries started only in May 1940. One of the first CXAM systems was placed aboard the USS California, a battleship that was sunk in the Japanese attack on Pearl Harbor on December 7, 1941.
United States Army
On June 30, 1930, the U.S. Army Signal Corps consolidated its widespread laboratory operations on Fort Monmouth, New Jersey and designated these the Signal Corps Laboratories (SCL), with Lt. Colonel (Dr.) William R. Blair appointed SCL Director Among other activities, the SCL was made responsible for research in the detection of aircraft by acoustical and infrared radiation means. Blair had performed his doctoral research in the interaction of electromagnet waves with solid materials, and naturally gave attention to this type of detection. Initially, attempts were made to detect infrared radiation, either from the heat of aircraft engines or as reflected from large searchlights with infrared filters, as well as from radio signals generated by the engine ignition. Some success was made in the infrared detection, but little was accomplished using radio. In 1932, progress at the Naval Research Laboratory (NRL) on radio interference for aircraft detection was passed on to the Army. While it does not appear that any of this information was used by Blair, the SCL did undertake a systematic survey of what was then known throughout the world about the methods of generating, modulating, and detecting radio signals in the microwave region.
The SCL's first definitive efforts in radio-based target detection started in 1934 when the Chief of the Army Signal Corps, after seeing a microwave demonstration by RCA, suggested that radio-echo techniques be investigated. The SCL called this technique radio position-finding (RPF). Based on the previous investigations, the SCL first tried microwaves. During 1934 and 1935, tests of microwave RPF equipment resulted in Doppler-shifted signals being obtained, initially at only a few hundred feet distance and later greater than a mile. These tests involved a bi-static arrangement, with the transmitter at one end of the signal path and the receiver at the other, and the reflecting target passing through or near the path. Blair was evidently not aware of the success of a pulsed system at the NRL in December 1934. In 1936, W. Delmar Hershberger, SCL’s Chief Engineer at that time, started a modest project in pulsed microwave transmission. Lacking success with microwaves, Hershberger visited the NRL (where he had earlier worked) and saw a demonstration of their pulsed set.
Back at the SCL, he and Robert H. Noyes built an experimental apparatus using a 75 watt, 110 MHz (2.73 m) transmitter with pulse modulation and a receiver patterned on the one at the NRL. In October 1936, Paul E. Watson became the SCL Chief Engineer and led the project. A field setup near the coast was made with the transmitter and receiver separated by a mile. On December 14, 1936, the experimental set detected at up to 7 mi (11 km) range aircraft flying in and out of New York City. Work then began on a prototype system. Separate receivers and antennas were used for azimuth and elevation detection. Both receiving and the transmitting antennas used large arrays of dipole wires on wooden frames. The system output was intended to aim a searchlight. The first demonstration of the full set was made on the night of May 26, 1937. A bomber was detected and then illuminated by the searchlight. The observers included the Secretary of War, Henry A. Woodring; he was so impressed that the next day orders were given for the full development of the system. Congress gave an appropriation of $250,000.
The frequency was increased to 200 MHz (1.5 m). The transmitter used 16 tubes in a ring oscillator circuit (developed at the NRL), producing about 75 kW peak power. Major James C. Moore was assigned to head the complex electrical and mechanical design of lobe switching antennas. Engineers from Western Electric and Westinghouse were brought in to assist in the overall development. Designated SCR-268, a prototype was successfully demonstrated in late 1938 at Fort Monroe, Virginia. Production of SCR-268 sets was started by Western Electric in 1939, and it entered service in early 1941. Even before the SCR-268 entered service, it had been greatly improved. In a project led by Major (Dr.) Harold A. Zahl, two new configurations evolved – the SCR-270 (mobile) and the SCR-271 (fixed-site). Operation at 106 MHz (2.83 m) was selected, and a single water-cooled tube provided 8 kW (100 kW pulsed) output power. Westinghouse received a production contract, and started deliveries near the end of 1940.
The Army deployed five of the first SCR-270 sets around the island of Oahu in Hawaii. At 7:02 on the morning of December 7, 1941, one of these radars detected a flight of aircraft at a range of 136 miles (219 km) due north. The observation was passed on to an aircraft warning center where it was misidentified as a flight of U.S. bombers known to be approaching from the mainland. The alarm went unheeded, and at 7:48, the Japanese aircraft first struck at Pearl Harbor.
As mentioned previously, a radio-based device for remotely indicating the presence of ships was built in Germany by Christian Hülsmeyer in 1904. Often referred to as the first radar system, this did not directly measure the range (distance) to the target, and thus did not strictly meet the criteria for radar – but it was certainl;y a solid precursor. Over the following three decades in invention-rich Germany, a number of radio-based detection systems were developed, but none were true radars. This situation changed rapidly as World War II loomed closer, with three major initiatives establishing German Radar.
Gesellschaft für Elektroakustische und Mechanische Apparate (GEMA)
In the early 1930s, physicist Rudolf Kühnhold, Scientific Director at the 'Kriegsmarine (German Navy) Nachrichtenmittel-Versuchsanstalt (NVA—Experimental Institute of Communication Systems) in Kiel, was attempting to improve the acoustical methods of underwater detection of ships. He concluded that the desired accuracy in measuring distance to targets could be attained only by using pulsed electromagnetic waves. During 1933, Kühnhold first attempted to test this concept with a transmitting and receiving set that operated in the microwave region at 13.5 cm (2.22 GHz). The transmitter used a Barkhausen-Kurz tube (the first microwave generator) that produced only 0.1 watt. Unsuccessful with this, he asked for assistance from Paul-Gunther Erbslöh and Hans-Karl Freiherr von Willisen, amateur radio operators who were developing a VHF system for communications. They enthusiastically agreed, and in January 1934, formed a company, Gesellschaft für Elektroakustische und Mechanische Apparatemfor the effort. From the start, the firm was always called simply GEMA.
Rudolf Kühnhold (1903–1992) was an experimental physicist who initiated the research that led to the Funkmessgerät (radio measuring device – radar) in Germany. In September 1935, Kühnhold led a demonstration of his system given to the Commander-in-Chief of the Kriegsmarine. The equipment performance was excellent, and the apparatus was given the code name Dezimeter-Telegraphie or simply DeTe. From this time onward, GEMA had total responsibility for additional development of the system. The basic DeTe eventually evolved into the Seetakt for the Kregsmarine and the Freya for the Luftwaffe (German Air Force); these popular sets were used throughout the war. For the remainder of the war, most of Kühnhold’s research at the NVK was in underwater acoustic techniques, working closely with the firm Electroacoustik GmbH (ELAC) in Kiev. Founded in 1926, ELAC was the primary supplier of echo-sounding (sonar) equipment for the Kregsmarine, with a staff that peaked near 5,000.
Work on a Funkmessgerät für Untersuchung (radio measuring device for reconnaissance) began in earnest at GEMA. Hans Hollmann and Theodor Schultes, both affiliated with the prestigious Heinrich Hertz Institute in Berlin, were added as consultants. The first apparatus used a split-anode magnetron purchased from Philips in the Netherlands. This provided about 70 W at 50 cm (600 MHz), but suffered from frequency instability. Hollmann built a regenerative receiver and Schultes developed Yagi antennas for transmitting and receiving. In June 1934, large vessels passing through the Kiev Harbor were detected by Doppler-beat interference at a distance of about 2 km (1.2 mi). In October, strong reflections were observed from an aircraft that happened to fly through the beam; this opened consideration of targets other than ships. Kühnhold then shifted the GEMA work to a pulse-modulated system. A new 50 cm (600 MHz) Philips magnetron with better frequency stability was used. It was modulated with 2- μs pulses at a PRF of 2000 Hz. The transmitting antenna was an array of 10 pairs of dipoles with a reflecting mesh. The wide-band regenerative receiver used Acorn tubes from RCA, and the receiving antenna had three pairs of dipoles and incorporated lobe switching. A blocking device (a duplexer), shut the receiver input when the transmitter pulsed. A Braun tube (a CRT) was used for displaying the range.
The equipment was first tested at an NVA site at the Lübecker Bay near Pelzerhaken. During May 1935, it detected returns from woods across the bay at a range of 15 km (9.3 mi). It had limited success, however, in detecting a research ship, Welle, only a short distance away. The receiver was then rebuilt, becoming a super-regenerative set with two intermediate-frequency stages. With this improved receiver, the system readily tracked vessels at up to 8 km (5.0 mi) range. In September 1935, a demonstration was given to the Commander-in-Chief of the Kriegsmarine. The system performance was excellent; the range was read off the Braun tube with a tolerance of 50 meters (less than 1 percent variance), and the lobe switching allowed a directional accuracy of 0.1 degree. Historically, this marked the first naval vessel equipped with radar. Although this apparatus was not put into production, GEMA was funded to develop similar systems operating around 50 cm (500 MHz). These became the Seetakt for the Kriegsmarine and the Freya for the Luftwaffe (German Air Force). The two systems were generally similar, although the early Seetakt systems worked on a 50 cm wavelength (600 MHz), while Freya was designed for much longer ranges and used a 2.5 m wavelength that could be generated at high power using existing electronics. Kühnhold remained with the NVA but also consulted with GEMA. He is considered by many in Germany as the Father of Radar.
The Freya Radar System
These early systems proved problematic, and a new version using improved electronics at 60 cm wavelength (500 MHz) was introduced. Four units were ordered and installed on the Königsberg, Admiral Graf Spee and two large torpedo boats (which in German service were the size of small destroyers). The Admiral Graf Spee used this unit successfully against shipping in the Atlantic. In Dec. 1939, after heavy fighting during the Battle of the River Plate, the Admiral Graf Spee was severely damaged and the captain scuttled the ship in the neutral harbor off Montevideo, Uruguay. The ship sank in shallow water such that its radar antenna was still visible. British photos taken of the ship showed the mattress radar antenna of the Seetakt radar. This is the first time that the British had seen radar being used by the Navy. In 1940, the British started deploying ship born radar.
Seetakt Radar mounted on the superstructure of the Graf Spee, Montevideo, Uruguay, December 1939
These early-model Seetakt systems were followed in 1939 by a modified version known as Dete 1, operating between 71 and 81.5 cm wavelength (368 to 390 MHz) at 8 kW peak and a pulse repetition frequency of 500 Hz. Maximum range against a ship-sized target at sea was up to 220 kilometers (140 mi) on a good day, though more typically half that. Performance was otherwise similar to the earlier system, with a range accuracy of about 50 m. This was considerably more accurate than the guns they ranged for, which typically had spreads of over 100 m. It was also much better than the optical rangefinding equipment of the era, which would typically be accurate to about 200 m at 20 kms.
In 1933, when Kühnhold at the NVA was first experimenting with microwaves, he had sought information from Telefunken on microwave tubes (Telefunken was the largest supplier of radio products in Germany). There, Wilhelm Tolmé Runge had told him that no vacuum tubes were available for these frequencies. In fact, Runge was already experimenting with high-frequency transmitters and had Telefunken’s tube department working on cm-wavelength devices. In the summer of 1935, Runge, now Director of Telefunken’s Radio Research Laboratory, initiated an internally funded project in radio-based detection. Using Barkhausen-Kurz tubes, a 50 cm (600 MHz) receiver and 0.5-W transmitter were built. With the antennas placed flat on the ground some distance apart, Runge arranged for an aircraft to fly overhead and found that the receiver gave a strong Doppler-beat interference signal. Runge, now with Hans Hollmann as a consultant, continued in developing a 1.8 m (170 MHz) system using pulse-modulation. Wilhelm Stepp developed a transmit-receive device (a duplexer) for allowing a common antenna. Stepp also code-named the system Darmstadt after his home town, starting the practice in Telefunken of giving the systems names of cities. The system, with only a few watts transmitter power, was first tested in February 1936, detecting an aircraft at about 5 km (3.1 mi) distance. This led the Luftwaffe to fund the development of a 50 cm (600 MHz) gun-laying system, the Würzburg.
Luftwaffe Würzburg Radar
German Würzburg radar at the beach near Arromanches les Bain, Normandy, France, 22 Jun 1944
This is a Würzburg FuSE62 D (also known FuMG39T(D or FuG62 D) set-up, which is fully wired and was last operated in the early 1990s. On the main shelf we see from left to right: Main range display unit ANG62; then fine-range display EAG62; the frame on the right of it shows on top: SÜ62d Urechse (Sender-Überlagerer 62 d), below on the left the IF unit ZFV62 and to its right the pulse modulator IG62a (Impulsgerät 'Igel'). The control CRT is somewhere in the centre of its front-panel; right of it we see the main unit of Rehbock FuZG64 (Funkzielgerät). On the far right we see:a reconstructed NA I (High tension 8 kV & filament supply to LS180); above it is mounted NA II various voltage up to 2500 volt; left of NA II we see NA III (low voltage negative supply); left to it: the 'Pintsch carbon pile' regulator to stabilize the 180 V AC supplies, using the voltage swing between 220 V and 180 volt (the carbon pile-rings are more or less pressed together as to keep its output accurately at 180 volt a.c.)
On the upper shelf: The zinc-chromate coloured module on the left-hand side is a remote control box to the FuZG212 (range calibrator, BG212 Ln28257); right of it is a transport box to EBL1 and EBL2 (Lorenz blind approach landing system); on its right, the power meter (Leistungsmesser Ln20978) to Würzburg FuSE62 (FMG39T- FuSE63(FMG40Tand FuSE65 (=Giant Würzburg = Riese), its in built dummy-load and RF voltage meter works by means of the so-called 'compensation method' (the detected dc component is compensated by means of a calibrated dc voltage. Compensation occurs when there flows no equalisation current in either directions); the black unit right of it is the US Carpet (radar) jammer T85-/APT5 (March 1945) used against Würzburg or similar signals; on top of it you see the unit 190 being the British Carpet noise source (modulator); right to it you see the wave-meter to Freya type FM121; the grey box next to it is the British signal generator type 54; on top of it stands the German radar jammer to ASV signals type B400UK43 also known as 'Olga II'; right to it you see the wave-meter (Frequenzkontrollgerät 62 = Ln20232) and the NEG62 is to adjust the Zero pulse at the ANG62 main presentation screen display; just visible next to it we see the Würzburg (62/65) valve tester Röhrenprüfgerät 62, which also was used in conjunction with FuSE64 (Mannheim) radar system and maybe FuMG40T(Mainz) as well.
The above sourced from http://www.cdvandt.org/archives_pp1.htm
The Würzburg radar was the primary ground-based gun laying radar for both the Luftwaffe and the Heer during World War II with over 4,000 Würzburgs of various models produced. It had a maximum range of about 29 kilometers (18 mi), and was accurate to about 25 m in range. Würzburg used a 3m paraboloid dish antenna mounted on a wheeled trailer, and the dish could be "folded" along the horizontal midline for travel.
Several versions of the basic Würzburg system were deployed over the course of the war. The first, Würzburg A, was operated manually and required the operators to pinpoint the target by maintaining a maximum signal on their oscilloscope display. Since the signal strength changed on its own for various reasons as well as being on or off target, this was not very accurate, and generally required the use of a searchlight to spot the target once the radar had settled on an approximate position. Nevertheless one of the very first Würzburgs claimed a plane in May 1940 by orally relaying commands to a flak unit. An experimental Würzburg B added an infra-red detector for "fine tuning", but in general these devices proved to be unusable and production was discontinued.
Würzburg mobile radar trailer with the dish "folded" along the horizontal midline in the travelling position.
Würzburg C featured lobe switching to improve aiming accuracy. The C model was aimed by sending the signal out of one of two slightly off-centre feed horns in the middle of the antenna, the signal being switched rapidly between the two horns. Both returns were sent to an oscilloscope display, slightly delaying the signal from one of the horns. The result appeared as two closely separated "spikes" which the operator attempted to keep at the same height on the display. This system offered much faster feedback on changes in target position, and since any change in signal strength would affect both lobes equally, the operator no longer had to "hunt" for the maximum signal point. An almost identical system was used in the United States' first gun-laying radar, the SCR-268.
The Würzburg D, introduced in 1941, added a conical scanning system, using an offset receiver feed called a "Quirl" (German for whisk) that spun at 25 Hz. The resulting signal was slightly offset from the centreline of the dish, rotating around the axis and overlapping it in the centre. If the target aircraft was to one side of the antenna's axis, the system would see the strength of the signal grow and fade as the beam swept across it, allowing the system to move the dish in the direction of the maximum signal and thereby track the target. Additionally, the area of the maximum signal can be made smaller than the beam width antenna itself could provide, leading to much improved accuracy. Würzburg D's accuracy was on the order of 2 degrees in azimuth and 3 degrees in elevation. In-service units were generally upgraded to the D model in the field. Even the D model was not accurate enough for direct laying of guns. In order to provide the system with much greater accuracy, the FuMG 65 Würzburg-Riese ("Giant Würzburg") was developed. Based on the same basic circuitry as the D model, the new version featured a much larger 7.4 m antenna and a more powerful transmitter with a range of up to 70 kilometers (43 mi). Azimuth accuracy was 0.2 degrees and elevation 0.1 degree, more than enough for direct gun-laying. The system was now too large to be carried on a truck trailer, and was instead adapted for operation from a railway carriage as the Würzburg-Riese-E, of which 1,500 were produced during the war. The Würzburg-Riese Gigant was a very large version with a 160 kW transmitter, which never entered production.
Another Würzburg radar - this one manned
Within Finland, Nokia and Tigerstedt also played a role in WWII radar countermeasures
During the 1950s, a security inspection of the Nokia Radar administration building found crates of World War II top secret documents in a secure area. The documents were ordered to be burned. Many a story went up in smoke - lost to history. However, not every top secret story is lost. Eric Tigerstedt, the Nokia radar pioneer, recounted a number of stories in 1968. At Nokia, the engineers were continually developing the latest radars and the improving the older units with new components. They were also doing analysis of captured enemy electronic equipment as well as of British and American-supliued radar requipment. One reason was to improve Nokia equipment with any improvement the enemy of our allies had made. The other, and most important reason, was to figure out methods to confuse the enemy equipment. This is called electronic counter-measures. If you could develop a new countermeasure you could make millions of dollars of enemy equipment as worthless as old junk.
The first electronic countermeasures laboratory was in the top floor of the old Nokia Radar building. Some of the work benches and specially designed cages are still there today, 70 years later. The Germans had radar units connected to anti-aircraft guns. One type was the "little Würzburgs." The Germans had over 8,000 of these effective units. Many American and British (and later, after we joined the war against the Germans, Ilmavoimat) planes were shot down by this deadly combination. Tigerstedt tells us, "Our soldiers captured one in Eston ia and it was quickly air freighted over the Gulf so we could study it and learn better how to use countermeasures against it. Unfortunately, the German crew objected to the 'liberation' of this particular set, and when our boys insisted, in a fit of temper, the Germans fired a fusillade of bullets into the critical parts of the set. "The set came to me, and soon our engineers were able to replace all broken parts except for the most critical one, a cathode-ray'' tube the likes of which we had never seen in this country. It was a complex multi-electron gun affair. I called a friend at Fenno Radio, who had often helped us on cathode ray tubes problems. Within hours, he was down in the area and we went over the problem - or rather looked at the pieces. "`I'll try,' he said, and we put all the pieces we could find into paper bag and he took them back to his plant. Selecting his best engineers, he put them on three shifts, and away they went. Four days later, he called me and said he had six identical tubes available and they would work. Shortly afterward, we had the Würzburg operational, and moved rapidly to discover its weaknesses, and there were some."
This is where Tigerstedt ends his account. Possibly the aircraft that would rain aluminum foil strips along the old Highway by Malmo Airport were working with the Nokia engineers to counter the captured repaired enemy unit. These strips would reflect the radar signals and fill the radar operator’s screens with thousands of dots. Which dot to aim at was the problem the Nazi radar and gun operators now faced. Sadly, this captured Würzburg Radar was not saved for history. The good news is many Finnish, American and British aircrews survived the war thanks to countermeasures developed by Nokia, with the help of Fenno Radio. Today, many are grandfathers who feel they were lucky to survive the German anti-aircraft flak, however, little do they know about how the experts at Noikia Radar made their luck for them.
Since before the First World War, Standard Elektrik Lorenz had been the main supplier of communication equipment for the German military and was the main rival of Telefunken. In late 1935, when Lorenz found that Runge at Telefunken was doing research in radio-based detection equipment, they started a similar activity under Gottfried Müller. A pulse-modulated set called Einheit für Abfragung (DFA - Device for Detection) was built. It used a type DS-310 tube (similar to the Acorn) operating at 70 cm (430 MHz) and about 1 kW power, it had identical transmitting and receiving antennas made with rows of half-wavelength dipoles backed by a reflecting screen. In early 1936, initial experiments gave reflections from large buildings at up to about 7 km (4.3 mi). The power was doubled by using two tubes, and in mid-1936, the equipment was set up on cliffs near Kiel, and good detections of ships at 7 km (4.3 mi) and aircraft at 4 km (2.5 mi) were attained. The success of this experimental set was reported to the Kriegsmarine, but they showed no interest; they were already fully engaged with GEMA for similar equipment. Also, because of extensive agreements between Lorenz and many foreign countries, the naval authorities had reservations concerning the company handling classified work. The DFA was then demonstrated to the Heer (German Army), and they contracted with Lorenz for developing Kurfürst (Cure Prince), a system for supporting Flugzeugabwehrkanone (Flak, anti-aircraft guns).
Summary of the state of German Radar in late 1939
From the above, we can see that the Kriegsmarine was beginning to be equipped with the Seetakt radar systems (and in 1939 by a modified version known as Dete 1) with a Maximum range against a ship-sized target at sea was up to 220 kilometers (140 mi) on a good day, though more typically half that, and a range accuracy of about 50 meters (this was considerably more accurate than the guns they ranged for, which typically had spreads of over 100 m. It was also much better than the optical rangefinding equipment of the era, which would typically be accurate to about 200 m at 20,000 meters). About 200 Seetakts were built. They were installed on warships and also used, in fact in greater numbers, for coastal defense. There was an attempt to fit Seetakt to U-boats, but it didn't prove practical. The Kriegsmarine had Seetakt in operation on their surface vessels months before the British or the Americans had operational radar on any of their warships. However, this progressiveness was only due to the initiative of a few officers who didn't make policy, and otherwise the Kriegsmarine's radar effort suffered from the same problem that would afflict Germany's technical efforts all through World War II: little or scatterbrained direction from the top.
The Kriegsmarine regarded radar as a low priority and were conservative in their specifications, insisting on reliability and simplicity at the expense of capability. They wanted Seetakt to be used primarily for ranging, with detection of vessels and obstacles in night and foul weather as a secondary objective. Precision fire-control was not an objective, at least initially. There were related problems at the bottom. GEMA didn't have experience at building electronic systems for the harsh shipboard environment and had to suffer through a painful learning curve. The low priority of their work also meant that they had to deal with poorly trained crewmen, a problem compounded by the fact that demands for secrecy kept detailed documentation, such as circuit diagrams, out of the hands of users for some time. The effort was generally left to fumble on its own.
Another element that hobbled German military technology development was interservice rivalry. This existed, always has and always will, in the military services of other nations, but the Kriegsmarine kept their work a complete secret from the rival service branches. Hermann Göring didn't find out about the Kriegsmarine's work until July 1938, and he was outraged that he hadn't been informed of it. He was more or less told that what the Kriegsmarine did was none of the Luftwaffe's concern, and that if the Luftwaffe wanted radars they could get them themselves. As it turned out, Wolfgang Martini quickly got in touch with GEMA to obtain Freyas for the Luftwaffe, though the Kriegsmarine did everything they could to interfere and would continue to try to block Luftwaffe access to GEMA through most of the rest of the war.
The Würzburg radar was the primary ground-based gun laying radar for both the Luftwaffe and the Heer during World War II with a maximum range of about 29 kilometers (18 mi), and accurate to about 25 meters in range. Even the Wuerzburg A was very accurate, and the Army was highly impressed. While the Lorenz company had also been working on a gun-laying radar, the military chose the Telefunken design and had it put in production. The Freya Radar, which was used by the Luftwaffe as an early warning radar, had a maximum range of only 160 kilometers (100 miles) and could not accurately determine altitude, making it inferior to Chain Home in those respects, but it was a fully steerable and mobile system. Over a thousand would be built in all during the war.
The Germans were clearly ahead of the British and Americans in the technical capabilities of their radar systems, with the German radars unarguably the most sophisticated of their generation, the Freya much more the shape of things to come than the British Chain Home, and the Wuerzburg clearly superior to any other gun-laying radar before the SCR-584. They produced the biggest range of radars, with finer resolution, better capabilities, more rugged construction and greater versatility than anyone else except the Finns before the outbreak of WW2. Yet clearly the Germans did something wrong. In fact, they did many things wrong. The most critical mistake was to overemphasize technical innovation and take the operational innovations necessary to use the new equipment effectively for granted (or rather, to ignore the concurrent requirement for technological change). They had a gaggle of competing agencies in this field, as in others, that did not communicate well with one another. They were slow to match the insight of the British in setting up the well-organized filter room system. Up until early 1940, radar had been not much more than a toy to most of the German brass and the early Freya’s were being used as part of the existing ground observer network, which featured nothing as well thought-out as the British filter room scheme, but ideas were floating around for improvements.
Renowned German historian, Harry von Kroge has written “The aspect of the German effort that seems to have differed from the Allied was the degree to which corporate rivalry affected the course events. The numerous agreements that had to be made concerning licensing and post-war rights in order to smooth production will certainly seem remarkable to American and British readers”, he went on to say that “a puzzling aspect of German radar research was the delay imposed by severe secrecy in drawing on the many excellent universities and polytechnic institutes until late in the war”. His claim was that the British and, to a lesser extent, the American radar effort ran more smoothly because it was under the auspices of the military with full access to all of the academic and civilian sources of expertise. His claim has some merit. Germany’s first radar array was developed by a private company with the encouragement of a major naval research institution. This contrasted with Germany’s other top scientific programmes such as missile development. Engineers assigned to rocket and propulsion development usually drew freely on the expertise of others, specially on the universities ranks, to achieve their goals. Again, there is evidence to support the theory.
It’s true that the British main radar problem, the development of a workable and reduced microwave-based system was enormously enhanced by the programme’s ability to recruit the best talent from any source. This, pluralistic effort would eventually find its way to a central research programme and thence to full production. In Germany on the other hand, there was not enough collaborative diversity, instead, a series of modern era monopolies worked under the cover of secrecy, not for military purposes but to protect their intellectual rights. This problem was compounded by Germany’s leaders’ preferences for offensive weapon systems instead of purely defensive ones such as a radar array. This mind set would have a devastating effect on the overall German war effort. But what is more puzzling about the whole programme was the lack of understanding of what a radar system could achieve by the very top political and military leadership. A clear example of this was the Luftwaffe’s technology chief, General Ernst Udet, who objected from the very beginning to the massive amounts of money the radar programme were being allocated on the basis that if it works “flying won’t be fun anymore”.
Runge noted in his memoirs that of course anti-aircraft fire was not exactly there to protect aircraft, moreover it was under the control of rhe army rather than the air force in those days “so perhaps his reaction was understandable, if not excusable.” One can extract from this episode not only the distress of a vanishing breed of WW1 pilots, but also a sense of the pervasiveness of interservice rivalry and the visceral preference for the offsensive spirit over technical advances in the defense of the Reich. The Germans also failed to use the technical advances in radar ro spur operational innovation, as we have noted previously. The Freya sets for example were viewed as an enhancement or replacement for the ground observer corps. R.V Jones, who was in charge of the on-going British assessment of German technical innovations during the war astutely observed:
“German philosophy ran roughly along the lines that here was equipment which was marvelous in the sense that it would enable a single station to cover a circle of radius 150kms and detect every aircraft within that range. Thus it could replace a large number of Observer Posts on the ground and so it was a magnificent way of economizing on the Observer Corps. Moreover, where we had realized that in order to make maximum use of the radar information, the stations had to be backed by a communications network which could handle the information with the necessary speed, the Germans seemed simply to have grafted their radar stations onto their existing observer corps network which had neither the speed nor the handling capacity that the radar information merited.”
Finland would not make the same mistake.
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A rather more extensive treatment of interwar British achievements in the field of radar is necessary to explain the interwar basis for the British victory in the Battle of Britain. At the same time, this will lay the foundations for an understanding of the similar but earlier victory of the Ilmavoimat in the Air War component of the Winter War (and we will examine this in a little more detail when we cover Finnish Radar development and use). Despite strong financial suppory for radar research from its inception in the UK, Britain lagged behind the Germans in technical change until 1940. They more than made up for the deficiencies in their systems however, by the manner in which they employed them. The distinction was understood and articulated by Churchill in his memoir if the Second World War, where he stated “…..we (had) turned our discoveries to practical effect, and woven all into our general air defence system. In this we led the world, and it was operational efficiency rather than novelty of equipment that was the British achievement.” (vol 1, The Gathering Storm, p.156).
This is an accurate assessment of the general situation with regard to Britain and displays a keen perception of the contrast between technical and operational leads in technologies, namely novelty of equipment versus effective adaptation of military thinking. However, Chruchill’s account is misleading in some ways. It does not mention that the British did not know that the Germans had a more advanced radar system, and it does not mention that the British believed they were more advanced both technically and operationally than the Germans. And it also does not mention that Finland had a radar system in operation that was superior to both Germany and Britains – in that it was both as technically advanced as the Germans and operationally at least on a par with the RAF’s. This was something that neither Britain nor Germany were in fact aware of until after WW2. Finland kept the Nokia Radar System a closely guarded secret while at the same time continuously improving their systems. The Finns received a number of American and British radar systems in 1943-44 as part of Lend-Lease aid, and on examination found these inferior to their own systems overall, although some components and component designs proved to be superior (these were quickly reverse engineered and incorporated into the Nokia Radar Systems). Post-WW2, the capabilities of the Nokia Radars came as a complete surprise to the US and British militaries.
However, returning to British radar, by the end of WW1, British military planners faced two strategic threats: the threat of submarine warfare, as had been experienced, and the looming threat of bombers. The first threatened to isolate Britain from the resources it needed, while the second threatened to destroy Britain from the skies. The initial response to the submarine threat was to continue work on the development of sonar techniques to find submarines. However, in the immediate aftermath of WW1, there seemed to be no defense against the bomber, and the psychological and political impacts of the German bomber attacks of 1917 and 1918 had been enormous. The suggestion in a newspaper in 1922 that the French had a bomber force outnumbering the RAF’s fighters was enough to create a public panic. A report by the air staff in 1925 that a French air offensive would cause more casualties in a few days than the Germans had inflicted over the entire course of WW1 with no prospect of an effective defense caused more panic.
And so, it was no wonder that both serving officers and civilians alike believed the conservative leader Stanley Baldwin when he proclaimed in the House of Commons in November 1932 that “the bomber will always get through.” Baldwin was in point of fact arguing for disarmament as the only feasible response, while the RAF was itself committed to building up its own bomber forces as a deterrent. The idea was not that air attacks would necessarily obliterate enemy cities but that they would be able to destry the enemy air fleet on the ground in their home country, along with the bases that they operated from. However, the RAF did not forget fighters. And in order to send up fighter aircraft against attacking enemy bombers, the enemy bombers needed to be located. In addition to direct observation, considerable research went into acoustic detection, using microphones and speakers to amplify the noise made by distant aircraft.
Acoustic detection of aircraft is now almost forgotten, but in the aftermath of WW1 and indeed, into WW2, it was a method of aircraft detection that was in widespread use.
Acoustic detection of aircraft
Here, a little aside to delve into the history of acoustic detection of aircraft. Before the advent of the aeroplane, acoustic location was applied to determining the presence and position of ships in fog. Acoustic location was used from mid-WW1 into the early years of WW2 for the passive detection of aircraft by picking up the noise of the engines. It was rendered obsolete before and during WW2 by the introduction of radar, which was far more effective. Horns gave both acoustic gain and directionality; the increased inter-horn spacing compared with human ears increases the observer's ability to localise the direction of a sound. There were three main kinds of system:
• Personal/wearable horns
• Transportable steerable horns
• Static dishes
• Static walls
Please note that much of the information and photos in this section are from http://www.aqpl43.dsl.pipex.com/MUSEUM/ ... ar/ear.htm.
Personable/wearable horns were perhaps the earliest examples, and the reason for their was to assist with navigation in fog. The image below is the earliest identified audio-location device, and is taken from the Scientific American, 1880.
Professor Mayers Topophone, Scientific American, 1880
Transportable steerable horns began to be seen a little later, becoming fairly widespread in WW1
A British Mk 1 Sound Locator: This model was used for location in the First World War, when aircraft flew relatively slowly and acoustic detection was a fairly practical proposition. It was manufactured by A.W. Gamage Ltd, who ran a famous department store in London specialising in toys, bicycles etc. (For Canadian readers, this example is in the Canadian War Museum, Ottawa).
A two-horn acoustic locator system at Bolling Field, USA, in 1921. The building in the background is the Army War College at Fort McNair.
A Czech four-horn acoustic locator: 1920s? There are two horns in the horizontal plane, and two staggered in the vertical plane. Scoop-shaped reflectors direct the sound into large-diameter tubes. Manufactured by Goerz. When tested at the Dutch military research station at Waalsdorp it was found it "contained fundamental deficiencies".
The height-locating half of the Czech four-horn acoustic locator. This picture is believed to be from the testing at the Dutch military research station at Waalsdorp.
A four-horn acoustic locator in England: 1938. There are two horns in the horizontal plane, and two in the vertical plane. The latter are at top and bottom left of the picture. Whether the horns were of crude flat wood construction as they appear to be, or if the flat panels were a protective casing for a more conventional horn remains a matter for speculation. This picture appeared in Popular Mechanics, Dec 1938. The caption describes the personnel as being from the Royal Engineers, (part of the British Army) but it seems more likely that they were actually from the Royal Observer Corps, who were civilians; however, the older chap on the right is wearing a distinctly military forage cap.
A four-horn acoustic locator again, in England: 1930s. Once more there are three operators, two with stethoscopes linked to pairs of horns for stereo listening. The exact method of operation is currently unknown, but perhaps as follows: the man on the left adjusts the mounting elevation until the aircraft noise is apparently central, while the chap on the right adjusts the bearing for the same result. The man in the middle reads bearing and elevation from dials and transmits it by telephone to the air defence system where the results from several locators can be combined to triangulate the target, and give its approximate height and position. Note that this version is not the same as that ine the previous photo. The two horizontal-plane horns are now on the same side of the tripod. This picture appeared in a book called Aerial Wonders of Our Time published in Dec 193?. The personnel here are definitely from the Royal Observer Corps. This was a group of civilian volunteers that had its origins in WW1.
A British sound locator crew working with a Search Light unit during the Blitz. Such methods, as well as the Observation Corps, were given considerable publicity and shown as part of the co-ordination of Air Raid detection. By contrast the Radar system, which was already playing a crucial role, remained highly secret.
Acoustic locators in Japan: 1930s. This remarkable picture is of an impressive array of Japanese war-tubas belonging to at least two acoustic locators mounted on 4-wheel carriages. It is a little difficult to work exactly what is connected to what, not least because the background appears to have been erased by some unsubtle retouching, but he format isprobably the same as the British model; there are two horns in a horizontal plane, and on one side of the mounting there are two more in a vertical plane. To the right, one of the figures is the Japanese emperor Horohito. Behind him are the AA guns intended to be used in conjunction with the locators. The only Japanese gun that seems to have been documented as being used with a sound locator is the Type 88 dual-purpose AA/coast-defence 75mm; there is not enough visible detail to verify that these are the guns shown in the picture, but they look about the right size.
Acoustic locators in Japan: 1930s. This picture appears to show the same war-tubas as the picture above. Note the Japanese characters on the side of trumpets. From the US magazine Mechanics & Handicraft, Jan 1936
Acoustic locator on trial in France: 1930s. This remarkable machine is an acoustic locator based on hexagons. Each of the four assemblies carries 36 small hexagonal horns, arranged in six groups of six. Presumably this arrangement was intended to increase the gain or directionality of the instrument. Once again there are three operators.
Another French sound locator.
Truck-mounted French sound locator….
another French sound locator….
“Members of the French Army man an acoustic locator device on January 4, 1940”. The device was one of many experimental designs, built to pick up the sound of distant aircraft engines and give their distance and location. The introduction and adoption of radar technology rendered these devices obsolete very quickly
And another French sound locator….Note the AA gun in the background
Polish Army Goerz sound locator (7 were bought in the early 1930’s)
Czech Army sound locator
A German RRH acoustic locator at an unknown location: 1940s? This apparatus was called the Ringtrichterrichtungshoerer (or RRH) which translates literally as "ring funnel direction hearer", or more accurately: "ring-horn acoustic direction detector". The RRH was mainly used in World War 2 antiaircraft searchlight batteries for initial aiming of the searchlights at night targets, presumably because it was cheaper and easier to make than a radar set. Later in the war they were replaced by radar sets. Like the British and French versions, the RRH was also composed of four horns, two to determine bearing, and two for elevation, arranged in a ring. The two lateral horns have a horizontal bar across their mouths
The RRH acoustic locator with operators at their posts. The RRH could detect targets at distances from 5 to 12 km, depending on weather conditions, operator skill, and the size of the target formation. It gave a directional accuracy of about 2 degrees. It had a crew of three - traverse aimer on the left seat, elevation aimer on the right seat and a dial-reader/talker in the middle. The rolled-up material above the operators' heads could be unfurled to provide shelter. The curved things visible under the ring are the rear of the horns.
The German RRH acoustic locator again. This gives a better view of the rear of the horns, curved for compactness
A US Army sound locator in use: 1943. This photograph was dated January 1943, and was presented by the American media as being current equipment. This was another piece of misinformation as radar sets were already in widespread use for searchlight control at that date. Note the large diameter acoustic tubes leading to the operator's headset. It should be said that the first Japanese air raids on the American-held island of Corregidor in late December of 1941 were detected by acoustic locators.
And as with most other armed forces of the interwar period, the Finnish military was also equipped with a range of sound locators. The photos below are from a range of sources but serve to illustrate that the Finnish militaries sound locator equipment was on a par with that in use throughout Europe at the time. Shown are Austrian Goerx m/39 and the Finnish Strömberg m/43 (license made in Finland from an Italian design by Strömberg Oy). Prior to the introduction of the first Nokia Radar Systems, there were five sound locators in service in Finland. These were used in conjunction with searchlight batteries but trials through the mid-1930’s had proved their usefulness to be minimal and no funding was allocated for additional sound location equipment.
Finnish military sound locator
Finnish military sound locator
Finnish military sound locator
Finnish military sound locator
Swedish Volunteers operating an acoustic locator in Finland in the Winter War, January 1940
(Photo taken from http://en.wikipedia.org/wiki/File:Antia ... n_1940.jpg, owner Carl Gunnar Rosborn, photo taken by his father)
Static Dishes and Static Walls
Steerable horns were inevitably limited in size, but a static dish could be much larger, giving more acoustic gain and the possibility of detecting aircraft at greater ranges. The first static dish was cut into a chalk cliff face between Sittingbourne and Maidstone in July 1915. Interestingly, the mirror was shaped to form part of a sphere, not part of a parabola, the latter always being used for radio aerials, searchlight reflectors, telescope mirrors etc. The part-spherical shape presumably gives better off-axis performance at the expense of on-axis precision, and it appears that all later static dishes and walls used a spherical/circular shape. The 1915 dish had a sound collector on a rotating mount at the "focal point". Over the 1920s and 1930s, many different sizes and types were tried in an effort to get the best possible results.
An acoustic locator dish in Kent, England: built 1928. This 30-foot high dish is located at Greatstone, Kent. The small concrete hut in front housed the operators. The vertical mast in the centre carried the acoustic pickup tubes. A static dish can be much larger than a fully steerable horn, giving more acoustic gain and the possibility of detecting aircraft at greater ranges. The pickup tube could be moved sideways to "steer" the direction of maximum sensitivity by a limited amount.
Sound Reflectors above Langdon Bay to the east of Dover
Sound Mirrors at Lade, Dungeness to the south west of Folkestone. Note metal pole in dish that carried the microphone. Also note Sound Wall at left background. The Dungeness mirrors, known colloquially as the "listening ears", consist of three large concrete reflectors built in the 1920s–1930s. Their experimental nature can be discerned by the different shapes of each of the three reflectors: one is a long, curved wall about 5 m high by 70 m long, while the other two are dish-shaped constructions approximately 4–5 m in diameter. Microphones placed at the foci of the reflectors enabled a listener to detect the sound of aircraft far out over the English Channel. The reflectors are not parabolic, but are actually spherical mirrors. Spherical mirrors may be used for direction finding by moving the sensor rather than the mirror.
An acoustic locator wall at Greatstone, Kent: built 1930. A mirror has to be much larger than the wavelength of what it is reflecting to work efficiently. This 200-foot wall was a later development designed to concentrate audio wavelengths in the 15 to 18 foot range, which were not handled effectively by 20-foot and 30-foot dishes. The wall could detect aircraft at 20 to 30 miles distance. This may not seem impressive, but in aircraft interception every second is valuable. With its later microphone installation the wall had a bearing accuracy of 1.5 degrees. However, the increasing speed of aircraft continually reduced the warning time and by the time the acoustic systems qwere abandoned, the warning of approach was less than 4 minutes.
It was the failure of these sound mirrors that gave an indirect but significant impetus to the development of radar in Britain. In 1934 a large-scale Air Defence exercise was held to test the defences of Great Britain and mock raids were carried out on London. Even though the routes and targets were known in advance well over half the bombers reached their targets without opposition. Prime Minister Baldwin's statement "The bomber will always get through" seemed true. To give time for their guns to engage enemy aircraft as they came over, the Army was experimenting with the sound detection of aircraft by using massive concrete acoustic mirrors with microphones at their focal points. Dr H.E. Wimperis, the first Director of Scientific Research for the Air Ministry, and his assistant Mr A.P. Rowe arranged for Air Marshall Dowding to visit the Army site on the Romney Marshes to see a demonstration. On the morning of the test the experiment was completely wrecked by a milk cart rattling by. Rowe was so concerned by this failure that he gathered up all the Air Ministry files on the subject of Air Defence. He was so appalled that he wrote formally to Wimperis to say that if we were involved in a major war we would loose it unless something new could be discovered to change the situation. He suggested that the best advisors obtainable should review the whole situation to see whether any new initiatives could be found. On 12th November Wimperis put this proposal to the Secretary of State and a Committee was set up under Henry Tizard, as we will cover a little later in this post.
By 1935 it was clear that radar was going to be a much more effective way of detecting aircraft, and all British work on the sound mirrors was stopped, and the funding diverted to radar research. However, interest in the sound mirrors was briefly revived in 1943 when it was feared that Germany might have developed an effective method of jamming the British coastal defence radar stations. British Post Office engineers made tests at the Greatstone mirror to see if the mirrors could be used after all in case of emergency. Improved electronic equipment in the detectors meant that it was now possible to detect enemy aircraft as far as 50 miles out. In the event, radar stations were never effectively jammed and the sound mirrors were never needed. Britain never publicly admitted it was using radar until well into the war, and instead publicity was given to acoustic location, as in the USA. It has been suggested that the Germans remained wary of the possibility of acoustic location and this is why the engines of their heavy bombers were run unsynchronised, instead of synchronised as was the usual practice, in the hope that this would make detection more difficult.
Nevertheless, there were long-lasting benefits. The acoustic mirror programme, led by Dr William Sansome Tucker, had given Britain the methodology to use interconnected stations to pin point the position of an enemy in the sky. The system they developed for linking the ranging stations and plotting aircraft movements was given to the early radar team and contributed to their success in World War II.
In Finland, as in other countries, acoustic locators continued to be used through the Winter War and into WW2, but as the Nokia Radar Systems proved their effectiveness, no further effort was put into building new sound locators or devising an improved model.
Note: If this is a subject that interests you, there’s even a book on the subject, “Echhoes from the Sky: A Story of Acoustic Defence” by Richard Scarth. It’s pretty much the only book on the subject and somewhat hard to track down at a reasonable price but you might get lucky…..
Next Post: The Netherlands: A Case Study in the development of Acoustic Sound Locators, and then back to the main topic again…..British Radar
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This is an actual case study I picked up online, published in 2009 in the Netherlands and a fascinating read on the subject. Some of it here and there repeats stuff I have already mentioned but for the purposes of reproducing the original document, I’ve included.
Development of Dutch sound locators to detect airplanes (1927-1940)
By A W M van der Voort and Ronald M Aarts (TNO-D&V Den Haag, The Netherlands, Email: firstname.lastname@example.org and Philips Research, HTC 36, 5656AE Eindhoven, The Netherlands, Email: Ronland.M.Aarts@Philips.com)
The first sound locator was invented by Alfred Mayer ; see Fig.1, and named the “topophone.”
Figure 1: Alfred Mayer’s topophone
It was used to determine the direction of sjips in the fog. In 1880 the topophone appeared in the popular press like the Scientific American in 1880. It eben appeared on a fake stamp; see Fig. 2, which was designed by the artist Ben Mahmoud .
Figure 2: A fake stamp
Mahmoud named “Owen Plumbly” as the inventor in 1832. Both the name and year are wrong .
From the First World War until the 1930’s air acoustics played an important role in air defense. As radar was still to be discovered, vision had to be supplemented by hearing using the sound of the engines. In the 1920’s, at least a dozen different acoustic locators for airplanes from different countries were available on the military market, see Figs 3-5.
Foreign Sound locators
In the late 1920’s the Dutch Army was not satisfied about the performance of the foreign sound locators they had in use for airplane detection. Therefore the Measurements Building at the Plain of Waalsdorp in The Hague started an investigation on three of these systems.
Figure 3: The half of the Goerz, Czechosolvakia
Figure 4: Barbier, Bernard and Turenne, France
Figure 5: Doppelt Richtungshorer, Germany
These locators had two pick-up elements for determination of the chart angle (azimuth) and two for the measurement of the elevation. The transport of sound from each pickup peair to a corresponding pair of human ears was carried out by means of metal or rubber tubes. Each pair was adjusted until the two ears received the sound signals at the same time. This occurs when the locator is pinting in the direction of the incoming sound. The locator was manned by two listeners, one for observation of the chart angle and one for the elevation.
Initial acoustic research
J.L. van Soest started his investigations of the human capability of hearing the direction of a sound source in 1927 [5-8]. Of great importance for determining direction is the time difference between the signals received by each ear. This could be tested with the “listening tube”, a rubber tube with wooden ear pieces at both ends. The tube was tapped with a knife around and on the centre-mark of the tube. The listener had to report whether he heard the sound from the left, the right, or straight ahead. To improve the accuracy, the tube was cut into two parts and a brass bar was mounted in between the two tube ends. Due to the higher velocity of sound in brass than air, a higher accuracy could be obtained . Very good listeners were able to perceive a time difference of one microsecond around the central mark on the tube. This appeared to be a factor of ten more accurate than the values measured by v. Hornbostel and Wertheimer earlier. This corresponds to a chart angle accuracy of about one degree. After testing the impulsive sounds, sinusoidal sounds were tested by putting a tuning fork on the tube . Subsequently, her performed listening tests in the free field . In this research one of the conclusions was that small head movements improved sound localization considerably. Further investigations stufied the sound path on the air, finding that it is dependent on temperature gradient, humidity gradient and wind speed . Most times these effects have a greater misdirection of a sound source than one degree.
Figure 6: Inflatable cushion for listening tests present in the army museum 
Disadvantages of the foreign sound locators
Van Soest determined various disadvantages of the present locators, among those are: 1. The wide base is not necessary, the ear base is sufficient. 2. Multipath effects of the sound through the metal or rubber tubes make a sound signal weaker and mear it out in time. 3. The great weight of the device meant manoeuvring could make a significamt amount of noise. The targegt could be lost; this was noticed by others as well, see . 4. The observations of two listeners (chart and elevation) had to be coordinated. 5. The forein locators were very expensive.
In the Measurements Building a new sound locator was developed. A parabolic sound mirror with a cross section of 120cm was cut in two halves and each was focused directly at an ear of the listener, see Fig. 7. Each hald was closed by a side plate with a hole on the place of focus of the paraboloids. Comparative tests showed that this arrangement performed much better that the current foreign equipment.
Figure 7: Sound locator Waalsdorp
The half paraboloids were joined to a vertical colum to which a seat was mounted for the listening operator. Around the ear-holes bearings were mounted for elevation movement. An inflatable ring shaped rubber cushion filled the space between bearings and the ears of the listener. The adjustment of the chart angle in the horizontal plane around the column and the elevation movement took place by muscle force of arms and legs. Helped by flat partition walls in each paraboloid the operator could reach an accuracy of less than two degrees in elevation using sound intensity. The advantages of Waalsdorp’s locator were 1/ Better observation and sharper indication of the sound source. 2. Lightweight system. 3. Movable without bearing noise. 4. One listener for chart angle and elevation. 5. Cheaper than the foreign systems.
To avoid wind noise a transparent jute cover was used (Fig. 8., below).
Figure 8: Listening tent
Because the airplane speed is not negligible with respect to the speed of sound in air, the actual location of the airplance differes from the location inferred by trhe operator. A correction cylinder was used to find the real direction. A reading operator handled this cylinder. The listening operator aimed the device towards the incoming sound of the airplave and by pressing a button he marked at least three successive positions in chart and elevation.
Figure 9: Flat projection of the template with several possible target paths and on path M 3 marks of an airplane. Horizontal the chart angle (azimuth), vertical the elevation.
These markings appeared as ink dots on the outside wall of the glass correction cylinder.
Figure 10: Correction cylinder
Inside the glass cylinder was a cylinder with a target paths template. The reading operator rotated the template cylinder to find a best fit of the three (red) markings to one particular (M) target path. The reading operator made an extrapolation dependent on airplane speed and the position of the last mark on the template (M track). With this extrapolationfrom the last marking along the chosen target path the corrected values foir chart angle and elevation was found.
Transport of angle values
The cound locator co-operated with field glasses and a searchlight. It was important the the chart angle and elevation of the airplane were quickly available at the field glasses and later on at the searchlight. Therefore an elecytrical transport systems (step system) was developed, see Figs 11-13. The values for chart angle and elevation established by the reading operator were directly available at the field glasses. The operator of the field glasses used these values to locate the plane and made adjustments to the chart and elevation angles to account for the real position of the airplane. These adjusted values were directly available at the searchlight. The time taken for the listener to make the last marking, till the switching on of the searchlight had to be short and consistent. When the angles were received the light was switched on to catch the plane.
The Dutch industry produced around one hundred of this type of sound locator.
Figure 11: STEP system
Figure 12: Sound locator in operation.
Figure 13: Field glasses
As airplane speeds increased it was no longer possible to realize reliable extrapolations. A new sound locator and searchlight had to be developed. The new searchlight was a searchlight with three axes, see Gig. 14. The airplance was detected visually by sweeping the searchloight beam over an area of sky. They used an altitude plave (Dutch “standvlak”, see Fig. 15). This plane was oriented so that it incorporated the straight airplane track and the position of the searchlight. When the chart angle and the elevation of the “standvlak” were known, axis 1 of the searchlight was oriented to the chart angle direction and axis 2 to the elevation angle of the “standvlak.” When this was ready the map was switched on and the lamp house was rotated around axis 3 to locate the airplane.
Figure 14: Three axis searchlight
To find the chart and elevation angle a new sound locator was developed, a three axis locator with two floors. The top floor was for the listener and the ground floor for the reading operator. After the listener made the necessary three markings, the reading operator could read off the chart and elevation angle of the “standvlak” which were then sent to the searchlight. How many of these locators were constructed is unknow, but at least one remains in an Army museum.
Minaturized sound locators
In the 1930’s the possibility of a surprise intrusion of many hostile airplanes became apparent. This initiated the concept of a permanently operated early warning system (Air Watch) comprising many listening locations distributed over a wide area. This necessitated the availability of a device to trace the sound of incoming airplanes with better capabilities than the unarmed ear. The Measurements Building in The Hague was asked to investigate the possibilities. From 1930 different versions were tested and it appeared that a miniature version of parabolic reflectors produced the best results, see Fig. 16. From 1935 hundreds of these locators had been made for the Dutch Air Watch Service.
Figure 15: set-up
Figure 16: Minature locator
 Alfred M. Mayer, Topophone, US patent No. 224,199, Filed Sept 30 1879, Granted Feb 3, 1880
 A false explanation to the stamp is in: The newsletter of the Acoustical Society of America “Echoes” Vol. 13(1), p4, 2003
 Dan Russell, Plumbly stamp, The newsletter of the Acoustical Society of America “Echoes” Vol. 13(3), p4, 2003
 J.L. van Soest and P.D. Groot, Stereoacoustische geluidsbeelden en kleinst waarneembare tijdsverschillen (in Dutch), Stereophonic sound images and just noticeable time differences, Physica 9, pp 111-114, 1929
 J.L. van Soest, Richtingshooren bij sinusvormige geluidstrillingen (in Dutch), Directional hearing with sinusoidal vibrations, Physica 9, pp 271-282, 1929
 J.L. van Soest and P.D. Groot, Het richtingshoorenn in de ruimte (in Dutch), Directional hearing in free space, Physica 11, pp 103-116, 1931
 J.L. van Soest, Rapport betreffende acoustische opsporing (in Dutch), Reporr on acoustical detection, unpublished report (in the TNO army museum collection), 1934
 Museum “Waalsdopr” – This musum reflects the histpry of TNO Defense, Security and Safety at location Waalsdorp (and its predecessors) since 1927, see http://www.museumwaalsdorp.nl/museum.html
 E.R. house: Reducing noise in airplane sound locators, J. Ac. Soc. Am..7,pp 127-134, Oct 1935
Well, there you have it on acoustic detection. And if you ever come across the TinTin comic with this illustration, you'll know what it is
And now it’s back to the main topic again…..British Radar
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And some additional background material….
After the First World War, the Air Clauses of the Versailles Treaty of 1919 were intended to end military aviation in Germany and to prevent the resurrection of the German Flying Corps. The Allied Control Commission oversaw the demobilization of the German Air Corps and the destruction of over 15,000 aircraft and 27,000 aero engines. A weakness in the Treaty of Versailles was the less strict restrictions against Germany possessing and manufacturing civil aircraft. Later, the Paris Air Agreement of 1926 removed all limitations on civilian aircraft manufacturing and commercial aviation. The Germans immediately expanded civil and commercial aviation establishing the foundations for a new air force.
General Hans von Seeckt, Chief of the Army Command at the Defence Ministry in 1920, was convinced that military aviation was the key to restoring Germany’s military power. He secretly selected a small group of regular officers from the army to oversee aviation concerns for the Ministry. This small group of officers consisted of future Luftwaffe notables such as Helmuth Felmy, Hugo Sperrle, Walter Wever, Albert Kesselring and Hans Jürgen Stumpff. As early as 1923, von Seeckt issued a memorandum arguing the need for an independent German air force. Von Seeckt made a number of astute political moves to ensure that the military could control the development of civilian aviation which would support a re-born Luftwaffe. In 1924 he had military pilots secretly training in civilian schools and managed to have a previous German Flying Corps officer, Captain Brandenburg, appointed as the head of the Civil Aviation Department.
The Paris Air Agreement of 1926 provided the veil behind which to secretly build up a new German air force. 1926 saw the birth of Deutsche Lufthansa with future Luftwaffe field marshal Erhard Milch as chairman of the corporation. Lufthansa, with generous government subsidies, played an important part in building infrastructure, training personnel, and developing aircraft industry for the future Luftwaffe. Lufthansa, in a short period, would become the most technologically advanced and experienced airline in Europe. When Hitler and the Nazi party assumed power in 1933, due to the foresight of the previously mentioned military officers, there was a nucleus of trained personnel and technical expertise to resurrect the Luftwaffe. After 1933, under the new political leadership, civilian production was secretly converted to military applications providing the aircraft to the new Luftwaffe. In March of 1935, Adolf Hitler and Hermann Göring felt that it was time to publicly announce the formation of the German Luftwaffe. Göring was appointed the Commander in-Chief of this new independent air force. Previously concealed flying clubs and police units were assigned to the new Luftwaffe forming a force of 1,888 aircraft and over 20,000 men at its inception. Now out in the open the Luftwaffe pursued a course of rapid build up and production of modern aircraft. The overt muscle flexing of the Luftwaffe caused deep concern across the English Channel and ultimately caused a critical rethinking of RAF defensive strategy.
Technical and Political Limitations
The rapid and ambitious Nazi rearmament program, as daunting as it appeared to observers, was limited by serious structural problems within the German economy and guided by geopolitical imperatives. Germany’s economic situation of the 1930’s was one of shortages of materials and hard currency to purchase these strategic items. The only natural resource possessed within Germany itself was an abundance of coal; everything else had to be imported. These items were bought with hard currency and were subject to blockade. To earn the hard currencies, the Germans had to maintain a strong industrial economy making export goods, which limited the size of rearmament programs. With the opportunity to build an air force from the ground up, Luftwaffe staff officers were as eager to promote strategic bombing as did their counterparts in America and Britain. Both Erhard Milch, State Secretary of the Air Ministry, and Walther Wever, the Luftwaffe Chief of Staff, felt that the Luftwaffe should provide a broad base of support to the other services, but maintained that the strategic bomber was the decisive weapon of air warfare. After Wever’s death in 1936, Milch took over the administrative and industrial tasks of creating the Luftwaffe. He discovered that the German aircraft industry lacked the designers and industrial capacity to create a strategic bombing fleet and concentrated on tactical and two engine bombers.
The fact that Germany was a continental power also impacted strategic thinking. In any conflict, the Germans faced the threat of immediate land operations. The Luftwaffe could not solely plan on waging a successful strategic aerial campaign without considering the threat of losing a land war. Hitler told his generals after coming to power that if France possessed any statesmen, she would wage war in the immediate future. The Luftwaffe’s strategic role from 1933–1939 was to deter both Poland and France from launching a preventive war against the Reich, further supporting the development of tactical aircraft and two engine bombers. Reflecting their commitment to Blitzkrieg, Milch and the German High Command felt that the best way to protect the country was through offensive air operations and not in defensive measures. U.S. Army post-war intelligence stated that Field Marshall Milch retarded development of aircraft warning and fighter control systems, because it did not contribute to the offense. Milch always planned for offensive actions and prevented any thinking, planning or action which would allow for extensive and adequate air defence.
The German High Command was focused on the strategic concept of smashing adversaries in short campaigns and the Luftwaffe developed a concept of purely offensive operations to fulfil their air defensive mission. A defensive war of attrition was to be avoided. The goal of the Luftwaffe was to drive enemy bombers away from their bases through offensive bombing campaigns making it less necessary to provide major air defence units for the Reich. What made the offensive argument more desirable was the economic realities of the time. Germany did not have the resources to pursue both an offensive and defensive strategy without taking forces away from the offensive arm. Luftwaffe planners fought any project that would threaten the build-up of offensive air power. This strategy fit well with Germany’s military tradition of the offensive being the best defence.
Lessons From Spain
During the rebuilding years of the Luftwaffe, the Spanish Civil War occurred and provided the testing ground for new aircraft and tactics. The Germans took many valuable lessons away from their involvement. Probably the most important lesson learned was the need for well developed coordination between ground and tactical air forces. Lt Col Wolfram von Richthofen, a cousin of Baron Manfred von Richthofen, recognized the need for close cooperation between ground and air forces. He was responsible for getting radios installed into tactical bombers and Luftwaffe liaison officers into ground units so that air units could be directly controlled by ground units. This concept of close air support provided another key element to the German’s offensive strategy of Blitzkrieg. Von Richthofen came under fire for his support of tactical air roles, which countered the views of the strategic bombing enthusiasts.
The Spanish Civil War also showed other problems with strategic bombing. The first problem was the difficulty of finding and hitting targets during both night and day. The fact that bombers were missing visible targets convinced Ernst Udet, Chief of all the Luftwaffe’s technical departments, that all bombers must be dive bombers to ensure satisfactory bombing accuracy. This flawed assumption would haunt future German bomber designs. At night and in bad weather, the Germans had trouble just finding the target and pursued radio directional systems. This resulted in the Knickebein system which was successfully used in the Battle of Britain. Other flaws in the strategic bombing theory became apparent during the Spanish Civil War. The Germans saw that fighters and civil defence measures were important, and could minimize the effects of strategic bombing. This heightened Germany’s interest in civil defence and prompted an increase in fighter production relative to bombers. Also one German observer noted that the bombing had a galvanizing effect on the population against Germany contrary to popular wisdom.
From their involvement in Spain, the Germans perfected the technique of close air support and validated the need for tactical air forces. The concept of strategic bombing became more unsettled, but highlighted the need for fighter aircraft and civil defence measures to counter the threat and the need for accurate bombing aids.
Development of German Radar - a quick revisit
In the drive to rebuild the Luftwaffe there seemed to be no real interest in developing a radio ranging device other than one to guide bombers to their target. Their focus was on developing offensive systems and it was only threatened nations, such as Britain, that felt an overriding need to counter the air threat. The British navy, on the other hand, was clearly superior to the German navy causing Germany to search for technological solutions to blunt the British naval superiority and prevent naval attacks. It is no surprise then that the German navy developed several of the best pre-war radar systems, as we have seen in a previous post. German industry in developing naval surface radar had unwittingly discovered the makings of modern air defence systems. There is no real evidence that the Luftwaffe ever pursued radar as a needed defensive device, but, once demonstrated, it purchased the units without much further thought to command and control issues. The combination of the Freya and Würzburg radar was especially powerful. Freya could be used in the classic role of a ground based search radar giving long-range early warning, and Würzburg could act as the acquisition radar for defensive weapons systems, whether it was a searchlight, anti-aircraft battery, or the vectoring of fighter aircraft.
The promise of technology and the reality were two different things. The Luftwaffe had accepted the equipment, but had never developed strategies to employ it. There is sufficient evidence that the German High Command knew the potential value of radar as an aircraft detection device as early as 1935. However, they viewed radar as primarily a gun sighting aid for flak and searchlight control. For these reasons, radar was initially assigned to flak units. General Wolfgang Martini, Luftwaffe chief of radio signals, after the war strongly stated that he realized the value of radar for aircraft warning and fighter control, but the high staff was unconvinced of his arguments. The staff was committed to the popular Blitzkrieg theory and discounted the need for air defence. On the offensive side, the Luftwaffe pursued radio and radar aids to bombing and navigation as a greater priority. The lessons of Spain proved the inefficiency of strategic bombing without accurate bombing aids. The Germans anticipated the problem of target finding and developed three electronic navigation and bombing aids. The German systems were Knickebein (‘Bent Leg’), X-Gerät (‘X-apparatus’), and Y-Gerät (‘Y-apparatus’). Because of these systems, the Germans were able to switch from day to night bombing without the loss of accuracy that Bomber Command later experienced.
Knickebein, Germany’s first navigational bombing aid, was originally developed in the 1930’s as an aircraft blind landing aid. It transmitted a beam in the 30 megahertz range composed of audible dots on one side and dashes on the other. The pilot flew along the beam with a solid tone marking the centre. Another beam was transmitted to mark the approach to and arrival over the target. The system was only theoretically accurate to within a kilometre and was susceptible to cockpit sounds and noise jamming. The X-Gerät system worked along the same principles, but introduced several improvements. It operated at a higher and more accurate frequency of 65/75 megahertz, used a mechanical indicator which was less susceptible to noise jamming, and provided an extra beam to calculate ground speed and determine bomb release. The theoretical accuracy of X-Gerät was improved to several hundred meters, but required the bomber crew to maintain a constant course, speed and altitude to achieve this result, something that was hard to accomplish in the heat of battle.
The final system Y-Gerät was the most sophisticated yet, but suffered from its own complexity. This system combined a radio beam with a modulated signal which measured distance. Theoretically, this system was very accurate, pin-pointing the exact location of the bomber and commanding the precise moment of bomb release. Unfortunately, the complexity of the modulated signal made it an easy target for jamming and the system never realized its potential in combat. Of the three systems X-Gerät seemed to be the most successful for the Germans. It was the least affected by jamming and provide a reasonable amount of accuracy. Probably the most significant achievement of the X-Gerät system was during November 1940 with the successful raids on Coventry. Popular post-war accounts speculated that Winston Churchill knew about the coming raids on Coventry from Enigma intelligence and elected not to evacuate the population to protect Enigma. More reliable sources contend that this story was pure fiction and that they never really solved how to adequately jam the X-Gerät signal to prevent the results at Coventry.
It is remarkable that the Luftwaffe which was so closely linked to tactical bombing developed these accurate navigation and bombing aids prior to the beginning of the war. The British strategic bombing emphasis failed to foresee this requirement and did not deploy it first navigation system, Gee, until March of 1942.
The Search for British Radar
In the spring of 1939 the Germans had their radar system working, Freya, and were curious if other countries had perfected this technology. German intelligence had discounted the French, Polish, and Soviets, but was worried about the British. It had been noticed that they were building 350-foot steel towers on the eastern English coast for some unknown purpose. The Germans had discounted that this was radar, since these antennas were not optimal for the radar frequencies that they were using. On the other hand General Wolfgang Martini, the Luftwaffe director general of radio signals, wanted to know what they were. German intelligence activities included Lufthansa aerial photos and an invasion of German tourists, who liked to sightsee and camp around Bawdsey Manor, the headquarters of the British research establishment, with portable radio equipment. All this intelligence revealed was that the towers were producing strong radio emissions and that there was a lot of activity around the manor.
Frustrated with these inadequate reports, Martini requested funding for twelve Zeppelin airships to monitor English radio signals. The Zeppelin was the only vehicle which could carry the required equipment and hover in place to take detailed measurements. Göring was not overly impressed with request and did not want to fund the project, but Martini out manoeuvred his boss and convinced the Secretary of State for Air, Erhard Milch, that this was a good idea. Milch agreed to release to Martini two dirigibles. Martini made two Zeppelin flights to England, but did not discover the secret of British radar. On the first flight in May of 1939 the crew did not observe anything significant, but noted loud continuous radio static source. The crew discounted this to be a fault in their radios. The second journey in August was just as disappointing because on that day the British radar chain was turned off to fix a malfunction. What is interesting is that instead of a radio malfunction on the first trip, the crew was probably receiving the static created by the British using high frequency (HF) for its radar signal. The Germans, early on, had discounted HF as a usable frequency for radar and concentrated on the VHF and UHF ranges.
The capabilities and doctrine of the Luftwaffe was a product of its times. Political imperatives and economic shortfalls forced planners to embrace the offensive solution and forego funding a creditable defensive strategy. Lessons from Spain spurred the development of very capable bombing and navigation aids which allowed for accurate night bombing, years before the British developed such a system. German scientists had independently developed the most advanced radar designs to that date, but had to convince the military of its usefulness. Even when the systems were purchased, the Luftwaffe leadership failed to grasp its true utility and saw it in the limited role of an accurate gunsight. Only after their offensive strategy had failed during the Battle of Britain and facing an increasing Allied bombing pressure did the Luftwaffe rethink its strategy.
Royal Air Force Doctrine
The Royal Air Force came into being on 1 April 1918 in a whirlwind of wartime development. From its beginnings, the RAF adapted to reflect its times and the political realities of the day. Lord Trenchand, the first and longest serving Chief of the Air Staff, ensured the survival of the embryonic air force. Trenchard, in the early 1920’s, had to prove that the RAF was cost effective and touted its benefits in maintaining colonial influence through revolutionary ideas such as air occupation to control large areas of territory. He also viewed air power as a way to attack an enemy’s moral will and avoid the costly ground campaigns associated with previous conflicts. Trenchard stated in 1928 that the air arm would be “best employed behind the battle zone at the sources of supply, communications, transport, and national morale.” RAF strategists seemed to allude to the fact that strategic air power could win wars alone and pursued doctrine along those lines. Trenchardian air theory would permeate the RAF, guide its organization and focus up to 1939, and indeed throughout the Second World War.
The Birth of British Radar
As the air threat from Germany increased, the Air Ministry argued that Britain needed to increase its emphasis on the air counteroffensive and that strategic air power’s ability to deliver ‘massive retaliation’ was an effective deterrent against aggression. The only problem with this argument was that Britain was extremely vulnerable to air attack. The Luftwaffe’s exponential growth in the 1930’s challenged the RAF’s ability to deliver a knockout blow or a credible counter offensive. In fact, the Luftwaffe’s rise imposed the spectre of the Germans delivering the classic strategic knockout blow to the RAF. The Air Staff’s reliance on a strategy of deterrence and counterattack started to worry government planners. As Britain entered the 1930’s civilian planners felt that there were only three possible strategies: First, follow the advice of the Air Staff and develop a bomber force large enough to be a credible deterrent; a second, and less likely course was to get rid of the bomber through international arms control agreements or, thirdly, to challenge the air theory directly, and pursue an effective deterrent against air attack, using recent developments in fighter aircraft and aircraft detection technology. The financial burdens of trying to maintain a strategic parity with the Germans threatened to bankrupt the military budget and the diplomatic failures in arms control forced the government to adopt the third strategy.
In response to Baldwin’s 1932 statement in parliament of that the bomber always gets through, and the RAF’s policy of counterattack, was a Frederick Lindemann, a leading scientist and test pilot, who in an article in The Times, August 1934, stated: “To adopt a defeatist attitude in the face of such a threat is inexcusable until it has definitely been shown that all the resources of science and invention have been exhausted.” Lindemann was not alone in his opinion, with Winston Churchill strongly supporting his position. The result of the political debate against the RAF policy of strategic interception, an offense-only strategy, and the defeatist attitude of “the bomber always gets through” resulted in the formation of a Committee for the Scientific Survey of Air Defence with Henry Tizard as Chairman in November 1934. Until 1935 the only means of aircraft detection with which the British had experimented was acoustical and infrared detection, both of which proved very unworkable and short ranged as we have seen. H. E. Wimperis, Director of Scientific Research at the Air Ministry and a member of the Committee, had read about Nikola Tesla's claim of inventing a 'death ray' which could either incapacitate the pilot, disable the aircraft motors, or detonate the bombs of an approaching airplane.
Watson Watt, now Superintendent of the Radio Research Station, Slough, was now well established as an authority in the field of radio, and in January 1935, Wimperis contacted him asking if radio might be used for such a device. Watson-Watt was certainly the right man to be asked. In 1915, he had joined the Meteorological Office and over the next 20 years, studied atmospheric phenomena and developed the use of radio signals generated by lightning strikes to map out the position of thunderstorms. The difficulty in pinpointing the direction of these fleeting signals led to the use of rotatable directional antennas, and in 1923 the use of oscilloscopes in order to display the signals. An operator would periodically rotate the antenna and look for "spikes" on the oscilloscope to find the direction of a storm. After discussing this with his scientific assistant, Arnold F. 'Skip' Wilkins, Watson Watt wrote back with a detailed analysis as to the futility of pursuing a death-ray weapon,, but added the following comment: “Attention is being turned to the still difficult, but less unpromising, problem of radio detection and numerical considerations on the method of detection by reflected radio waves will be submitted when required”. Over the following several weeks, Wilkins considered the radio detection problem. He outlined an approach and backed it with detailed calculations of necessary transmitter power, reflection characteristics of an aircraft, and needed receiver sensitivity. Watson Watt sent this information to the Air Ministry on February 12, 1935, in a secret report titled "The Detection of Aircraft by Radio Methods."
The Air Ministry
Reflection of radio signals was critical to the proposed technique, and the Air Ministry asked if this could be proven. A short twelve days after Watson-Watt had presented the memorandum, he successfully demonstrated his concept. To test this, Wilkins set up receiving equipment in a field near Upper Stowe, Northamptonshire. On February 26, 1935, a Handley Page Heyford bomber flew along a path between the receiving station and the transmitting towers of a BBC shortwave station in nearby Daventry. The aircraft reflected the 6 MHz (49 m) BBC signal, and this was readily detected by Doppler-beat interference at ranges up to 8 mi (13 km). This convincing test, known as the Daventry Experiment, was witnessed by a representative from the Air Ministry, and led to the immediate authorization to build a full demonstration system.
The Daventry Experiment 26 February 1935, set up by A.F.Wilkins and his driver, Dyer, to demonstrate the feasibility of Radar.
This breakthrough has been rather inaccurately hailed as the birth and invention of radar by numerous British historians. During the year of 1935 Dr. Watson-Watt perfected his new technology of radar moving his main research centre to Bawdsey Manor. Based on pulsed transmission, a preliminary system was designed and built at the RRS by the team. Their existing transmitter had a peak power of about 1 kW, and Wilkins had estimated that 100 kW would be needed. Edward George Bowen was added to the team to design and build such a transmitter. Bowens’ transmitter operated at 6 MHz (50 m), had a pulse-repetition rate of 25 Hz, a pulse width of 25 μs, and approached the desired power. Orfordness, a narrow, 19-mile (31 km) peninsula in Suffolk along the coast of the North Sea, was selected as the test site. Here the equipment would be openly operated in the guise of an ionospheric monitoring station. In mid-May, 1935, the equipment was moved to Orfordness. Six wooden towers were erected, two for stringing the transmitting antenna, and four for corners of crossed receiving antennas. In June, general testing of the equipment began. On June 17, the first target was detected—a Supermarine Scapa flying boat at 17 mi (27 km) range. In December 1935, the British Treasury appropriated £60,000 for a five-station system called Chain Home (CH), covering approaches to the Thames Estuary. The secretary of the Tizard Committee, Albert Percival Rowe, coined the acronym RDF as a cover for the work, meaning Range and Direction Finding but suggesting the already well-known Radio Direction Finding.
In March 1936 the work was transferred to the Air Ministry. At the new Bawdsey Research Station, the CH equipment was assembled as a prototype. Watson-Watts successes led him to propose a chain of radio detection stations spaced twenty miles apart around the coast. The positions of aircraft were to be established by triangulation from adjacent receivers. The Air Staff funded twenty of these stations and seven were in operation by August 1936. This was the beginning of the Chain Home (CH) radar network. The CH stations did not rely on new radio techniques, but drew on Watson-Watt’s experience with the British Broadcasting Corporation and high frequency (HF) radio. He proposed simple aerials on tall towers. The transmitter aerials ‘floodlit’ the airspace in front of them with pulses of radio energy which, when reflected from an aircraft, were picked up by the receiver aerial. The range of the ‘echo’ was directly measured on the face of the cathode ray tube and the position of the target could only be ascertained through triangulation from other stations with a radio direction-finding instrument, a goniometer.
There were equipment problems when the Royal Air Force (RAF) first exercised the prototype station in September 1936. These were cleared by the next April, and the Air Ministry started plans for a larger network of stations. Initial hardware at CH stations was as follows: The transmitter operated on four pre-selected frequencies between 20 and 55 MHz, adjustable within 15 seconds, and delivered a peak power of 200 kW. The pulse duration was adjustable between 5 to 25 μs, with a repetition rate selectable as either 25 or 50 Hz. For synchronization of all CH transmitters, the pulse generator was locked to the 50 Hz of the British power grid. Four 360-foot (110 m) steel towers supported transmitting antennas, and four 240-foot (73 m) wooden towers supported cross-dipole arrays at three different levels. A goniometer was used to improve the directional accuracy from the multiple receiving antennas.
Chain Home consisted of a series of enormous towers, 300 feet high which started to appear all along the coastline of Eastern Britain. It was the Chain Home system which was used to such dramatic effect during the Battle of Britain in 1940, to guide RAF Fighter pilots towards incoming German bombers.
By the summer of 1937, 20 Chain Home stations were in operation. A major RAF exercise was performed before the end of the year, and was such a success that £10,000,000 was appropriated by the Treasury for an eventual full chain of coastal stations. At the start of 1938, the RAF took over control of all CH stations, and the network began regular operations. In May 1938, Rowe replaced Watson Watt as Superintendent at Bawdsey. In addition to the work on CH and successor systems, there was now major work in airborne RDF equipment. This was led by E. G. Bowen and centered on 200-MHz (1.5 m) sets. The higher frequency allowed smaller antennas, appropriate for aircraft installation. From the initiation of RDF work at Orfordness, the Air Ministry had kept the British Army and the Royal Navy generally informed; this led to both of these forces having their own RDF developments.
At the outbreak of war in September 1939, CH had eighteen stations covering the eastern and half of the southern coast of Britain reporting to one Filter Room. The choice of HF imposed steep practical limitations on the system. HF, which is a relatively long wavelength, requires large antenna arrays to radiate sufficient power. Transmission at any one station required four 360-foot-high masts, 180 feet apart, between which the antenna wires were strung. The returned signal was not received by the same antenna, but on four separate 240-foot-high masts. To say the least the whole installation was extremely large. It could not rotate and did not scan, but floodlit a 100-degree sector with radiation. Detection of aircraft was possible only within the limits of the 100-degree sector and depended on the direction finding of the return signal from various antennas. The system was ineffective over land and was only suitable to a coastal location. The CH system was the only English radar system in operation at the outbreak of the war.
CH was a dead end approach to radar technology, whereas Freya would become the classic model of modern radar design. Freya was a mobile 360 degree radar effective over land and water, able to transmit and receive from the same antenna and able to resolve the target with a high degree of precision. The British failed to develop gun laying radar such as Würzburg, for flak batteries and Seetakt for naval guns, in the pre-war years. Even more telling, the RAF did not anticipate the need for navigational and bombing aids until confronted with German systems and their own inability to destroy targets with any reliability.
In tales of the Battle of Britain radar emerges as the sword that defeated the Luftwaffe during the ‘Blitz’. Radar was just a key component in the system of command and control that Dowding and his staff at Fighter Command developed. Their innovation was to meld the potential of radar into an integrated system of rapid counter-action against bomber attack. As important as CH was to the defence of Britain, the real hero was the unique development of the Filter Room which could sort all available intelligence and erect the best defence possible. Surprisingly, radar was not so unique, but the Filter Room at Bentley Priory was, playing a key role. CH stations were not effective in resolving and locating targets as was a Freya type radar which rotated and used a frequency five times higher.
The Filter Room helped to minimize the weaknesses of CH. It was able to collect, and resolve into a clear picture, what the actual threat was from the numerous overlapping radar plots reported from various stations and match fighter resources against the enemy. The British had developed a lead over the Germans in the method in which they used radar information, but not in the equipment itself. Radar was just a component of the air defence picture. Spotting reports and signals intelligence filled in the areas where radar could not see, aircraft over 120 miles away and behind the radar station. In many ways signals intelligence was just as valuable to the British as was CH radar. With signals intelligence the British were able to repeat their naval successes of World War I in the new field of air combat.
The receiver block at Bawdsey
Signals intelligence allowed radar to report the approach of aircraft which were already expected. CH was able to give a twenty minute warning to the fighters to intercept their target, but the radar was not sensitive enough to resolve the number of aircraft or type. German air communications were intercepted at British HF listening stations. Early in the war German fighters used HF radio telephony while the bombers used more traditional HF telegraph for communications. From the interception of this traffic, the British could get up to a two hour warning and detailed information on aircraft numbers, routes and identity of attacking formations.
Probably the biggest failure of the British radar effort was their inability to believe that the Germans had radar and the view that their technology was superior. This refusal to speculate on the existence of German radar is curious, given the amount of intelligence available. Such evidence included a detailed scientific report spirited to London from Norway, the Oslo Report, which detailed German developments in radar and rockets. It was discounted as a ruse and only after these revolutionary technologies were discovered was the report re-examined. The British also had photo intelligence of the radar array on the scuttled pocket battleship Graf Spee and the empirical evidence that their bombers did not get through at Wilhelmshaven, combined with the ability of German searchlights, fighters and flak to find their aircraft at night.
In 1931, at the at the Woolwich Research Station of the Army’s Signals Experimental Establishment (SEE), W. A. S. Butement and P. E. Pollard had examined pulsed 600 MHz (50-cm) signals for detection of ships. Although they prepared a memorandum on this subject and performed preliminary experiments, for undefined reasons the War Office did not give it consideration. As the Air Ministry’s work on RDF progressed, Colonel Peter Worlledge of the Royal Engineer and Signals Board met with Watson Watt and was briefed on the RDF equipment and techniques being developed at Orfordness. His report, “The Proposed Method of Aeroplane Detection and Its Prospects,” led the SEE to set up an “Army Cell” at Bawdsey in October 1936. This was under E. Talbot Paris and the staff included Butement and Pollard. The Cell’s work emphasized two general types of RDF equipment: gun-laying (GL) systems for assisting anti-aircraft guns and searchlights, and coastal- defense (CD) systems for directing coastal artillery and defense of Army bases overseas.
Pollard led the first project, a gun-laying RDF code-named Mobile Radio Unit (MRU). This truck-mounted system was designed a small version of a CH station. It operated at 23 MHz (13 m) with a power of 300 kW. A single 105-foot (32 m) tower supported a transmitting antenna, as well as two receiving antennas set orthogonally for estimating the signal bearing. In February 1937, a developmental unit detected an aircraft at 60 m (96 km) range. The Air Ministry also adopted this system as a mobile auxiliary to the CH system. In early 1938, Butement started the development of a CD system based on Bowen’s evolving 200-MHz (1.5-m) airborne sets. The transmitter had a 400 Hz pulse rate, a 2-μs pulse width, and 50 kW power (later increased to 150 kW). Although many of Bowen’s transmitter and receiver components were used, the system would not be airborne so there were no limitations on antenna size.
British Army. GL mark II, 5m gun laying, receiver British Army. GL mark II, 5m gun laying, receiver. The set had three dipoles: one at right and left for direction by swinging the whole assembly; a third that moved vertically for height determination. Although classified as "gun laying," it had little or no blind-fire capability. Deployed only in 1940.
Primary credit for introducing beamed RDF systems in Great Britain must be given to Butement. For the CD, he developed a large dipole array, 10 feet (3.0 m) high and 24 feet (7.3 m) wide, giving much narrower beams and higher gain. This could be rotated at a speed up to 1.5 revolutions per minute. For greater directional accuracy, lobe switching on the receiving antennas was adopted. As a part of this development, he formulated the first – at least in Great Britain – mathematical relationship that would later become well known as the “radar range equation.” By May 1939, the CD RDF could detect aircraft flying as low as 500 feet (150 m) and at a range of 25 mi (40 km). With an antenna 60 feet (18 m) above sea level, it could determine the range of a 2,000-ton ship at 24 mi (39 km) and with an angular accuracy of as little as a quarter of a degree.
Although the Royal Navy maintained close contact with the Air Ministry work at Bawdsey, they chose to establish their own RDF development at the Experimental Department of His Majesty’s Signal School (HMSS) in Portsmouth, Hampshire, on the south coast. The HMSS started RDF work in September 1935. Initial efforts, under R. F. Yeo, were in wavelengths ranging between 75 MHz (4 m) and 1.2 GHz (25 cm). All of the work was under the utmost secrecy; it could not even be discussed with other scientists and engineers at Portsmouth. A 75 MHz range-only set was eventually developed and designated Type 79X. Basic tests were done using a training ship, but the operation was unsatisfactory.
In August 1937, the RDF development at the HMSS changed, with many of their best researchers brought into the activity. John D. S. Rawlinson was made responsible for improving the Type 79X. To increase the efficiency, he decreased the frequency to 43 MHz (7 m). Designated Type 79Y, it had separate, stationary transmitting and receiving antennas. Prototypes of the Type 79Y air-warning system were successfully tested at sea in early 1938. The detection range on aircraft was between 30 and 50 mi (48 and 80 km), depending on height. The systems were then placed into service in August on the cruiser HMS Sheffield and in October on the battleship HMS Rodney. These were the first vessels in the Royal Navy with RDF systems.
Royal Navy Radar: Diagram to show the operation of radar at sea in trapping enemy bombers. Aircraft have been caught in the Radar beam of a warship. Plane 'A' which is not fully in the beam, is seen by the radar operator as the smaller inverted 'V' in circle, but plane 'B' in the full beam is seen by the radar operator as the largest inverted 'V' on the right circle. The 'hump' on the left is the radar transmission signal.
In 1939, as we have seen, a number of countries were working on Radar and had radar systems in various stages of development. However, of these countries, other than Finland, only Britain had developed a working Radar Network and integrated this into air force operations. The use of Chain Home in the Battle of Britain over the Summer of 1940 proved to be an essential factor in the RAF’s victory – and it was well publicized later. However, it was NOT (as it is often portrayed) the first time in history that an electronic early warning and control system was used in an air battle with decisive effect. That honor belongs to the highly secret and even now little known Nokia “Kotka Silmissä” (Eyes of the Eagle) Radar System which was, in 1939, by all measures the most effective radar system in operation in the world at the time.
In discussing the effectiveness of “Kotka Silmissä,” we should interject a brief explanation of terminology. Technology is often analyzed in terms of patterns of change in phases: invention, research, development and innovation, each following the other in a complex sequence with various feedback loops. Innovation typically involves market considerations. A distinction should also be made between innovation (as the spread of a new “best practice”) and diffusion (as a closely connected but later phase where the best practices becomes “average practice”). Adaptation is primarily associated with the innovation phase, while the introduction of new military doctrine is in general closely associated with the diffusion phase. Here, it is also useful to distinguish technical, operational and technological change during each of these phases. “Technical Change” can be understood as a matter of equipment, or physical devices. The introduction of a radar set per se involves a “technical change”. An “Operational Change” involves the function of the radar set or system and the procedures for their employment. The way in which technical changes and operational changes interact with each other evolves as experience is gained and “best practices” are determined. Technological Change on the other hand the new context that emerges from the interaction of technical and operational change with each other and with the environment. To understand radar as transforming the context of combat is to conside the emergence of a new logic. Technological innovations are thus understood as changes in the environment for determining the best practices involving mission considerations.
It is also useful to note the role of strategic goals as perceptual filters. The Germans emerged from WW1 with the desire to challenge the international status quo. The German policy was essentially a grand strategic offensive in which aircraft, submarines and tanks – the most potent offensive weaponry to emerge from WW1 – were key elements. Radio communication greatly enhanced the effectiveness of these weapons systems by providing a means of command and coordination of fast-moving or far-flung formations. Although the Germans maintained their WW1 preference for radio telegraphy aboard bombers and ships, including submarines, they placed great emphasis on equipping their single seat aircraft and armoured units with voice radio sets and radio networks to link units and echelons. They also continued to have great faith in encryption techniques. Radar, perceived as fundamentally defensive, received some technical, less operational, and even less technological consideration until well into WW2. The Germans planned to be on the offensive and to know by radio where there forces were. They also expected to use signals intelligence to determine the locations of enemy forces.
The British meanwhile, were on the grand strategic defensive after WW1. They placed a great emphasis on signals intelligence, which had already proved its worth. For this reason, they also expected their own, and enemy, policy to emphasize radio silence. Radar offered a form of intelligence of great defensive value and the British perceived it as a technical, operational and technological response to German threats. British radar systems became a technical countermeasure to aircraft and submarines. Radar employment patterns became operational countermeasures to German bomber or wolfpack deployment procedures. And radars ultimate purpose was as a technological countermeasure – a form of grand strategic reponse – to the technological changes in the mobility and velocity of combat made possible by the radio coordination of enemy air and sea offensive formations.
At least until 1939, and in some ways until 1940, the Americans also had a stake in maintaining the international status quo but acted as if they did not realize it. In effect, American policy was grand strategic indifference. The result was slow and unfocused adaptation to the changes wrought by both German and British radar developments, until it appeared in 1940-41 that Germany would be successful; in altering the international configuration of power. The Americans only then lurched towards a more definitive strategy and began to accelerate technological innovation.
And next of course, we wil finally get to take a look at Finland, Eric Tigerstedt and the Nokia R&D Team’s Radar Detection System Project
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And on that note,
All the best for Christmas and a Happy New Year..........Nigel
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Today most people know something about radar and that it played a vital role during the Second World War, and if they’re British, particularly during the Battle of Britain. In this age of television, cell phones, computers, E-mail, electronic banking and the Internet, radar is generally taken for granted as an important tool for the navigation of aircraft and ships, as well as for use in weather forecasting and in military hardware. However, few know how, in the Second World War, Finland developed its own radar which first proved invaluable both in helping the Ilmavoimat to command the skies during the Winter War and which proved equally as valuable in helping the Merivoimat protecting the vulnerable Baltic and North Atlantic shipping routes. There are two primary reasons for this lack of knowledge – the first being that Finnish Radar was kept so secret that very few members even of the Finnish armed forces had any idea that it was being used. Security was tight, radar personnel were very carefully selected, minimal records were kept and most war historians found no information about it, then or now.
The second reason has been the inaccessibility of historical information to war historians, both Finnish and foreign – as with much of the detail on Finnish history in WW2, primary source material is in Finnish and as such, has been relatively inaccessible to the foreign researcher and given the sparsity if information even in Finnish, almost all Finnish war historians have also missed the work that went on in this area, instead reflecting the common belief that the radar equipment used in Finland was all sourced from foreign suppliers. This has meant that most studies of Radar in WW2 have completely omitted mention of Finnish efforts in this regard, concentrating as they do in British, German and American sources. With most researchers simply unaware of the Finnish work in this area, no effort has been made to track down and translate Finnish historical material, an omission which is only now being corrected, unfortunately some 70 years on and with much original source material now destroyed and the principals involved no longer with us and available for interviews.
The impetus to introduce and use Radar
However, before walking through what we do know of the history of the Nokia Radar Project, a quick overview of the end result and its effects on the Winter War is likely useful for the uninformed. In earlier posts, we have covered and reviewed the initiatives underway around the world and the overall state of various countries radar programs in late 1939. And in retrospect, we can say that in late 1939, at the time of the start of the Winter War, the Finnish Nokia “Kotkansilmissä” (Eyes of the Eagle) Radio Detection System (later to be known as Radar, which is how we will refer to it from here on for simplicities sake) that was in operations was in terms of technical capability on a par with the best available in the world at that time (basically, that means on a par with the German equipment of 1939-vintage, thanks to Tigerstedt’s personal and largely informal access to the German scientists and companies involved) and certainly technically far superior to the equipment used by the British Chain Home Network at the same time. And indeed, visually, the Nokia radar systems were strikingly similar to the German (and the rather later US) radars, following also the same initial pattern of three basic types – a “long-range” mattress radar developed into two sub-types, one for air surveillance and one for maritime surveillance use, and a “short-range” radar used for AA gun, searchlight and naval gunfire control in conjunction with mechanical fire control devices (we will cover mechanical fire control devices in more detail when we come to look at AA guns).
On the other hand, as we have seen, the effective use of radar by Germany was greatly hindered by the “offensive” mindset and a lack of any interest in thinking through of the operational “best use” of such equipment. Finland by way of contrast was in a somewhat different strategic situation as has been mentioned frequently. Finland’s proximity to the USSR had resulted, perhaps not surprisingly from a military standpoint, in a strategically defensive mindset. This meant that much Finnish air defense thinking was focused on both defensive weapons and operational procedures to enhance air defence effectiveness, whilst at the same time maintaining a tactically offensive and highly aggressive combat mindset. Radar as a technical innovation meshed in easily with Finland’s strategically defensive mindset and once the technical capabilities of the new tool were proven, a great deal of attention was paid to inter-weaving the new tool into the existing air defence organisation and structure in order to achieve the best possible result. This was not without it’s challenges, but the small size of the Finnish military and the “we can do it” approach that had been engendered through the decade of the 1930’s encouraged a “let’s try it and see what happens, we can always try something else if it doesn’t work” approach.
Within the Ilmavoimat, both the Commander, Kenraaliluutnantti (Lieutenant-General) Aarne Somersalo and the recently appointed chief of the newly formed Fighter Command, Eversti (Colonel) Richard Lorentz, were highly supportive of the initiative. A new Ilmavoimat unit, the Radio Measuring Battalion (Radiomittauspataljoona, Rad.Mitt.P) commanded by the newly promoted Majuri H. Rautvuori (of whom we will see more), was formed on 3 October 1938, with the objective of operationally integrating the Radar equipment into the Ilmavoimat’s air defence system. In this, as in many other aspects of Finland’s air defences, Somersalo was somewhat of a visionary. He had the patience to listen to scientists and engineers as well as his Ilmavoimat pilots and specialists. He was a man who asked questions until he understood exactly what was being proposed, learning more about the technology of air defence than perhaps any other senior air officer in the world, perhaps with the single exception of Sir Hugh Dowding, head of the RAF’s Figher Command from 1936 (as an aside, Dowding had early in his flying career actually been the first man to send a radio signal from an aircraft to the ground).
Somersalo was a personable sort of a chap, he could easily have become a politician and indeed, seriously considered this in the early 1930’s before deciding, with Mannerheim’s support and encouragement, to stay on as head of the Ilmavoimat. And on the subject of air warfare, by the mid-1930’s he was an expert in the field who knew exactly what he was talking about and he was ably assisted by a small group of talented subordinates who were all experts in their field. Somersalo was focused on the threat of air attack from the Soviet Union, although not quite to the exclusion of all else, and the entire focus of his career was to ensure that Finland was as well-defended in the air as could possibly be achieved with the means at hand. As with the closest of his subordinates, Eversti Richard Lorentz, he had in his head an airman’s three-dimensional sense of how to fight a battle in the skies over Finland, and he came to understand that it would involve combining the newest and most radical ideas about radio direction finding on a grand scale with the latest kinds of radio communications equipment and with high performance fighter aircraft into an efficient, tightly controlled, well-led organisation linking fighters, antiaircraft guns and ground observers into a single fighting unit. And with those who did not share his vision or, in the late 1930’s, his sense of urgency, Somersalo could be very bloody-minded indeed. And in this attitude, he could count on the support of Mannerheim, who himself kept up to date with the technology of warfare.
Somersalo felt this growing sense of urgency from mid-1937 on. Involved as he was in the selection and briefings for the Ilmavoimat volunteers who flew and fought in the Spanish Civil War, he took a strong interest in the information that was fed back, particularly in the reports and analysis from his protégé, Lorentz, who for a lengthy period commanded the Ilmavoimat volunteers in Spain. As with Mannerheim, whose protégé he himself had to some extent become, Somersalo too felt the hot winds of war at his back, urging him on to prepare the Ilmavoimat for a battle he was sure was coming. And despite doubt, interference and to some extent hostility (particularly from those who, still espoused the Douhetist theories of strategic bombing despite its sheer impossibility for Finland and despite the Ilmavoimat’s own experimental results which had proved in detail the wild inaccuracy of high-level bombing), Somersalo persevered in his vision for the Ilmavoimat and, as it would prove, he succeeded just in time.
His technical expertise was the impetus that led him to his whole-hearted support of Eric Tigerstedt’s work in developing Radar as well as to the acquisition of the latest Fighter, Bomber and Ground-attack aircraft that would help the Ilmavoimat control the skies. His technical expertise and his vision of the air battles to come resulted in the construction of the “brain” of the Ilmavoimat, the futuristic Air Operations Room at Mikkeli which was in constant touch with the network of radar plotters, ground controllers, similarly constructed Ilmavoimat Sector Operations Rooms and the Ilmavoimat Squadrons themselves across the length and breadth of Finland. It was an Operations Room from which the air battle could be systematically observed, controlled and led.
And Somersalo was also a man who believed that “the bomber would NOT always get through.” And this is an important point to make. In 1937, as the Nokia Radar research and development program kicked off, Somersalo, Lorentz and Magnusson, the three architects of the Finnish air defence system, were in a tiny minority within the greater world of aviation in believing that “the bomber would NOT always get through.” That the bomber WOULD always get through was the accepted wisdom of the 1920’s and 1930’s. Towards the end of WW1, the Germans had made a major effort to bomb London and the coastal cities of the south of England with their squadrons of large Gotha biplane bombers, hoping to weaken British resolve through a terror-bombing campaign. Compared with what happened in WW2, the damage and the number of deaths were small but the bombing campaign itself made a huge psychological impression. (Personally, I can vouch for this – my Grandmother lived in Hull and as a 10 year old, her parent’s house was destroyed by a bomb from a Zeppelin – luckily for me the family were all out at a Church function – but the only thing that survived was a glass paperweight sitting on the mantelpiece of the fireplace which she kept and which I now have – it was a story she told many times when I was young and it very obviously had made a huge impression on her).
Once the war was over, and aircraft gradually started to become larger and more powerful (although even in the mid-1930’s, bombers still resembled those of WW1 more than they did those of WW2 that we are all familiar with), the belief grew that the “next” war would begin with huge bombing raids that would annihilate whole cities on the first day. This illusion was in part the work of military propagandists for “strategic bombing” such as General Giulio Douhet in Italy and General Billy Mitchell in the United States, and in part also the work of senior air officers who promised politicians that a big force of bomber aircraft would serve as the best deterrent to war and would be much cheaper to build up and maintain than a large army. This was an argument that appealed both to those who “sought peace” and to those who sought economy in governmental spending.
Of course, nowhere did those fleets of bombers exist, least of all in a small country such as Finland. And as Somersalo caustically commented any number of times with regard to the “bomber proponents” within Finland, “If every single one of our military aircraft was a bomber, we still wouldn’t have enough bombers to flatten even 5% of Leningrad alone.” Strangely enough, the idea of the bomber as the ultimate weapon became more widely accepted in Britain than in any other country. The French military was not that interested in bombers, indeed, Marshall Foch was quoted as saying “Aviation is a sport – for war its worth zero.” The Germans for their part dreamed primarily of rebuilding their army. The Soviet Union relied on its millions of soldiers. Within the UK, the idea of the bomber as the weapon of the future moved rapidly from being a military theory to being a widespread idée-fixee in the mind of the public, thanks largely to the immense power of the poular press, radio and films. A 1936 film, “The Shape of Things to Come,” based on the book by H G Wells, began with the destruction of a major European city (recognizably London) by a huge fleet of bombers which darkened the sky, had an immense effect on the public and on the UK government (and indeed, apparently deeply impressed Hitler).
The idea that the bomber would always get through was helped along by the development in the mid-1930’s of a range of “fast bombers” that were faster than the fighters designed to intercept them. Between 1933 and 1935 both the British and the Germans were infatuated with this concept. In the UK, the rather eccentric millionaire Lord Rothermere, owner of the Daily Mail newspaper and an aviation enthusiast, ordered “the fastest private transport plane in the world” from the Bristol Aircraft Company. This was a twin-engine all-metal monoplane which could carry six passengers and a crew of two at the then unheard of speed of almost 300 miles per hour. When it was delivered to him in 1935, he gave both the aircraft and the design to the Air Ministry as a patriotic gesture. The Air Ministry then modified the plane, which became the Bristol Blenheim Mk I bomber. The Blenheim was faster that any fighter then existing, as indeed were its rivals, the German Dornier Do17, the Heinkel He111 and the Junkers Ju88. The problem with all of these aircraft, however, was that they carried a relatively light bomb load, made up of fairly small bombs. Even the largest of them, the He111, could carry only eight 500lb bombs held nose upwards in a modular rack like eggs in an egg container. This seemed like a reasonable bombload in the mid 1930’s and even Somersalo was caught up in the enthusiasm for these aircraft, although he did not favor them above all else as some advocated. (As we have seen, the Ilmavoimat did buy a number of Blenheims and also manufactured them under license – into WW2, Blenheims were one of the major bomber-aircraft types within the Ilmavoimat).
But unlike the “bomber advocates”, Somersalo could think rationally about the possibility of defending Finland against aerial attack, and in investing in the advanced technology and complex ground organisation that would be needed to detect and destroy enemy bombers and to protect Finnish civilians and soldiers from attack from the air. And in building up a strong fighter force, Somersalo found it easier to sell fighters to the politicians than bombers. Even the minority of SDP politicians who were in favor of “collective security” and strong believers in the League of Nations were less offended by spending money on fighters rather than on bombers. At least fighters were be definition for defense, not attack, and it was hard even for the SDP’s pacifist fringe to argue that having the ability to defend oneself if attacked was morally wrong (although some made a gallant attempt to do just this). A single fighter aircraft cost perhaps 20% of the price of a large bomber and in addition, fighters could fly from grass or ice strips, whereas bombers because of their weight generally required long and expensive concrete runways, bigger hangers and more men to fly and maintain them, all of which was an enormous cost.
That Somersalo used this argument to his advantage can be seen in the aircraft types procured by the Ilmavoimat through the 1930’s. Somersalo used Ilmavoimat funding to largely procure Fighters and also Bombers more suited to the ground attack, tactical support and dive-bomber role rather than to strategic bombing – and even the Blenheims, bought partially to appease the “bomber advocates”, fitted into this category, being able to operate off rough strips. The Ilmavoimat did procure a small number of larger aircraft as we shall see when we conside the post-Munich Crisis procurement program, but these were generally purchased for specific purposes and the Ilmavoimat certainly never possessed anything like the Lancaster or the American Flying Fortresses. That said, Somersalo guided and drove the creation of Finland’s air defence system from the ground up. He strongly backed Tigerstedt’s work to develop Radar and was instrumental in ensuring the funding to build an interlaced network of radar stations from eastern Karelia along the Gulf of Finland to the Åland islands. He drove through the purchase of the best fighter aircraft Finland could buy, as well as strongly pushing the buildup of factories in Finland to manufacture aircraft engines (notably the Merlin and the Hispano Suiza) as well as aircraft cannon (again, Hispano-Suiza). He insisted that all “his” aircraft be fitted with high-frequency wireless sets, enabling pilots to talk to each other and to communicate with the ground (this at a time when many airforces still used visual signals or wireless telegraphy with a radio operator in the aircraft). And it was his vision that resulted in the inter-linked network of what we would now call “real-time” communications from ground observers and radar stations to both Area Air Defence Centres (Ilmapuolustusaluekeskus) and to the central Air Operations Center at Mikkeli which controlled the overall air war and which allowed real-time information to be transmitted to the pilots in the air in terms that they could understand in order to effectively intercept the enemy.
Like many visionaries, Somersalo could be impatient, but he also intuitively understood that large-scale changes would meet with suspicion and hostility even from those who would benefit most and so he took the time to explain, persuade and convince the men and women of the Ilmavoimat as well as the politicians and the senior officers of General Headquarters. Fighter pilots were initially appalled at the idea that they would be told where to fly and what to do over the radio by young women – for Somersalo had already come to the conclusion that the only way he could lay his hands on enough additional personnel to transmit the endless flow of information from the radar stations to the Ilmavoimat Air Operations Room and from there “filter” it out to the Area Air Defence Centres (Ilmapuolustusaluekeskus), and from these to the squadrons and pilots in the air, would be to employ large numbers of young women (initially the young Ilmapuolustusaluekeskus women in question were often themselves the wives of the fighter pilots and other squadron personnel who were Lotta Ilmavalonta volunteers).
On the whole, it was amazing how few of these Lotta Ilmavalonta volunteers buckled under the strain over the course of the Winter Wat itself. They all realised the importance of their work and it took a really major illness to prevent them from appearing for duty. However, subsequently, time took its toll of some amongst that small group. After the war, there were instances of suicide and of recourse to alcohol and bouts of deep depression. This is not to be wondered at when one considers that whilst filtering the tracks of the Ilmavoimat squadrons on operations in Finland and over the USSR or plotting fighter sorties against incoming hostiles, these young women knew that their own husbands or sweethearts were amongst the pilots and aircrews. They would count with trepidation the numbers of the returning Ilmavoimat aircraft and the messages from squadrons on losses as the aircraft landed after sorties and the radio operators among them were in real-time voice communication with the pilots. Given the skills, training and experience of the Ilmavoimat pilots, aircrew losses were relatively speaking, low. But still on occasion there would be a pale face among the Ilmavalonta personnel or a quick replacement (there was always a small pool of reserve personnel standing by for just this type of occurrence).
The Nokia Radar Project
As we have noted, the Nokia R&D Project began seriously in late 1937, when the Military R&D Oversight Committee proved receptive to Tigerstedt’s proposal for Radio Direction Finding, well supported by information gleaned by Tigerstedt on the current state of research and development in both the UK and in Germany - and by late-1937 Tigerstedt (and Nokia) had the funding needed to begin work. We know (as has been mentioned) that early in 1937, on having joined Nokia Radio and with R&D funding having been made available, Tigerstedt had visited the UK, where he spent considerable time with the British scientist and inventor, Baird, over a two month period where the two spent considerable time working on or theorizing regarding radio wave detection systems and applications for infrared technologies. At this later date, there is little evidence on whether or not Baird was connected in any way with the British Chain Home Radar project, but as it stands it would appear not as Tigerstedt’s Nokia Radar designs bear rather more than a fleeting resemblance to the German radar systems rather than the early British radar, making it more than likely that Tigerstedt utilized his informal contacts with the German scientific community to gain a significant head start.
Given the extreme secrecy under which research was conducted, the records of the Nokia Project that are available are spartan in detail. As mentioned, we know that work started in earnest in late 1937, by which time it appears that Tigerstedt had already completed the preliminary designs on paper at least. As has been mentioned, much of the theory behind radar was known and Tigerstedt had certainly either been provided with copies or had a thorough enough understanding of the German Frey/Seetakt radars to complete preliminary designs in detail. Immediately on Tigerstedt’s return to Helsinki, work started in the Nokia lab. The Nokia team, led by Dr B F J Schonland, had already acquired many of the necessary components from Nokia Radio (and had manufactured some components where necessary) and with the aid of Tigerstedt’s designs and copious notes from his meetings in Germany, in a couple of months and with much ingenuity, the team had completed an effective radar transmitting/receiving apparatus. They informally christened it the “ET01” (for “Eric Tigerstedt”).
The first Finnish radar transmitter, ET01, built by Nokia and successfully tested at ranges of up to 100km in early 1938.
In late December 1937, in an endeavour to receive reflected “echoes” from an aircraft, the Ilmavoimat was asked to fly an aircraft on a particular course at a fixed time. Nothing, however, appeared on the screen, leading the Nokia team to believe there were faults with their equipment or the design. As it turned out, the pilot - who of course had no idea as to the reason for his instructions - had diverted from the assigned course in order to wave to his girlfriend outside her house! Finally, in great secrecy on 29 December 1937 the team obtained their first weak echo from a test aircraft, at a distance of about 8 km away. After various modifications and adjustments, the ET01 recorded readings from some 100 km to the north and later it picked up aircraft at 60 km distance. Finland's first radar was operational.
Dr B F J Schonland, the leader of the Finnish radar development team (Schonland was one of Nokia’s leading research scientists and directly subordinate to Tigerstedt. He was largely responsible for the actual construction and field testing of the radar equipment used throughout the Winter War and WW2 and was assigned senior rank as a Lt-Col as an expedient measure to ensure cooperation from those not in the know but from whom cooperation was necessary).
The other key technical person connected to war-time radar in Finland was Eng. Yliluutnantti (Lieutenant) Jouko Pohjanpalo (1908-1992) who, after the war, became a Professor and the Director General of the State Telecommunications Laboratory for some decades. During the war, Yliluutnantti Pohjanpalo was responsible for the production of radar units at the State Electrical Workshop, Nokia Radar and Fenno Radio and worked closely with both Tigerstedt and Schonland on ongoing design modifications and improvements.
Work by the Nokia team to improve the apparatus continued and towards the end of April 1938, a workable production prototype seemed to be ready. On 14 May 1938 Kapteeni (Captain) H. Rautvuori (an Ilmavoimat officer assigned to the project), Yliluutnantti (First Lieutenant) Erik Boden and Ylivääpeli (Master Sergeant) Rajalin left Helsinki with two heavy vehicles containing equipment to set up a twin mobile ET02 on a coastal headland near Turku. Not surprisingly, the problems they encountered in Turku were daunting: Kapteeni Rautvuori found that neither the Maavoimat nor Merivoimat bases knew anything about them and that no accommodation, rations or, more importantly, helpers had been arranged. Eventually, four men were supplied to help, but they were unfortunately all classified as unfit for active service. One man had a broken arm, another had a chronic chest disorder, the third an awful skin disease and the fourth pneumonia!
Since these men could not be expected to provide assistance with the heavy digging and other necessary hard labour required, the Kapteeni, Yliluutnantti and Ylivääpeli set to work in atrocious weather conditions. Finally the station was installed and operational. Naval personnel at the adjacent Turku Signal Station helped with rations and accommodation. Kapteeni Rautvuori managed to obtain a more useful group as assistants and the set went on the air with Yliluutnantti Boden as its first commander. Good results were obtained immediately, when shipping was detected at about 30 km, but a violent storm demolished the aerials and a further four days were spent in repairing the damage. Thereafter things settled down and the ongoing trial went well with good results achieved in tracking both surface and air targets.
A drawing by Dr Schonland of Finland’s first experimental coastal radar station – an ET02 being trialed outside Turku (The original drawing is at the Finnish Museum of Military History, Helsinki) over May-July 1938.
With the ET02 being successfully trialled, Tigerstedt and Schonland turned their hands towards improving the design and setting up production facilities. To start with, the mobile radar concept was put to one side and a larger, stationary, set was designed with better range and performance. The operating frequency was adjusted to about 125 MHz. Two separate antenna assemblies, each consisting of 12 dipoles in two rows were used. The output power was 8 kW and the PRF was approximately 1,000 Hz. Individual bombers, flying at an altitude of 5,000 m were detectable at up to a distance of 70 km, the figure going down to 40 km at 2,000 meters, and for bigger formations (the type Soviets generally used) to 130 km. The distance uncertainty was 150 meters and the angular resolution 5 Degrees. Designated the Nokia NR01/38, further testing was carried our over September to November 1938, while at the same time the Ilmavoimat began to put an operational infrastructure into place, with Kapteeni (Captain) H. Rautvuori promoted to Majuri and placed in command of the Ilmavoimat’s newly formed Radio Measuring Battalion (Radiomittauspataljoona, Rad.Mitt.P). This unit would later be increased in size to a Regiment, with Rautvuori being further promoted and remaining in overall command. The Merivoimat would go on to form its own naval-oriented Radio Measuring Battalion focusing on surface surveillance, but the two organizations were at all times tightly meshed operationally, more often than not jointly operating the same stations, filter rooms and operations centres.
The “Kotkansilmissä” system, from Eric Tigerstedt’s ”concept”sketches
A hastily installed “Kotkansilmissä” Nokia NR01/38 antenna system, one of the first radar surveillance sets to become operational.
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By the autumn of 1939, equipment for 17 stations had been manufactured and assembled, with a chain of 8 “Kotkansilmissä” air and surface surveillance stations had been rapidly constructed stretching 400kms from Lake Ladoga to Viipuri and along the coastline of the Gulf of Finland as far eastwards as Turku – stations were constructed in carefully positioned locations outside Tolvajarvi (the north-easternmost position), Sortavalla, Käkisalmi, Viipuri, Kotka, Helsinki, Hango and Turku. In addition, 6 further stations were hastily built on islands in the Gulf of Finland in conjunction with the existing coastal defence positions (at Bjorke, Lavansaari, Someri, Mäkiluoto, Örö and north of Turku at Lypertö). In addition, equipment for a three further stations was constructed and stockpiled for the refortification of the old positions on Utö, Kökar and the Aland Islands in the event of war. With Finland moving to a war footing over the summer and autumn of 1939, numerous exercises were carried out to familiarize personnel with the system and its use. Initial attempts to use the radar system to direct Ilmavoimat fighters to discreetly intercept civilian aircraft did not go very well, but everyone learned, and “Kotkansilmissä” proved its usefulness during further exercises in September 1939. Ground controllers successfully directed fighter interceptors to their targets three-quarters of the time.
The early “Kotkansilmissä” Radar Stations were rapidly constructed over 1939, generally in Bunker Systems with towers to extend the range similar to the model illustrated above. Where stations were constructed on islands in the Gulf of Finland, they were co-located with pre-existing coastal defense batteries and defending infantry units. All radar equipment was fitted with demolition charges to be used in the event that the station was attacked and in danger of being captured.
A typical “Kotkassilmissä” radar receiver room of 1939
As has been mentioned earlier, Somersalo was instrumental in driving through the operational integration of the early radars into an effective air defence system. All radar users learned sooner or later that such a powerful tool was of limited use without the proper procedures in place to make good use of it. Radar was a new thing and the Ilmavoimat had to learn by doing as well as by theorising. Fortunately for Finland and the Ilmavoimat, Eversti Richard Lorentz and his introduction of the “Havaitse-Punnitse-Ratkaise-Taistele!“ (Observe-Weigh/Consider-Decide-Fight!") loop into combat proceduresmeant that operational tempo was a prime area of focus for the Ilmavoimat. The availability of real-time radar data meant that the faster flow of operational data to fighter squadrons on the ground, as well as to fighters in the air, was of crucial importance and this was an area that the Ilmavoimat immediately focused in on.
As with many other industrial nations, there was a significant interest in Finland in the 1920s and 1930s in what is now known as the “Efficiency Movement”. Majuri Rautvuori and Eversti Lorentz worked closely with two Finnish industrial efficiency “experts” to identify ways and means to improve the flow of information and efficiently control and direct air defence. The end result was a major improvement in the flow of communications, the filtering and direction of information and the integration of the air defence chain of command. And in fact integration of the air defence chain of command had been one of the primary problems identified by Somersalo even prior to radar being introduced, when a mid-1938 demonstration of an early prototype radar system had gone comically wrong even though the radar system itself had worked perfectly. Somersalo was well aware of the importance of a unified command, and with Mannerheim’s support, the Ilmavoimat was given direct and unifed control over all assets related to air defence.
An Area Air Defence Centre (Ilmapuolustusaluekeskus): Tellers on the balcony overlook the plotting table and vertical long-range handover board. At the end of the balcony a Leading Observer acts as Post Controller.The introduction of the “Kotkansilmissä” Radar Stations led to extensive improvements to the overall system that was already in existence, extending the range and allowing Controllers to provide real-time direction to Ilmavoimat fighters as they moved to intercept incoming or outgoing Soviet aircraft.
Perhaps the most significant operational innovation made by the Ilmavoimat was the introduction of the “Filter Room”. Since all personnel and records were under tight security, it is only recently that the story of the Ilmavoimat’s Filter Room has come to light – this was an aspect of the war that was even more obscure and tightly secured than the Nokia Radars themselves. Operationally, the large network of Observers generated a mass of information that was handled through Ilmapuolustusaluekeskus (Area Air Defence Centres) and the introduction of the Radar Stations introduced a flood of additional real-time data which needed to be assessed and used in real-time to be most effective. To be used most effectively, the mass of raw information generated by the radars had to be processed before it could be presented to the Operations Room. This processing was carried out by the “Filter Room”, which was the nerve centre of the Radar and visual surveillance system. The complexity of the Filter Room task cannot be overstated. Much depended on the Filterer’s detailed knowledge of the performance and limitations of each individual radar and their confidence in the ability of the crews on watch. The Filterer’s ability to correlate the information quickly and assess the probability of the true radar picture and of the visual observations being called in underpinned the successful operation of the whole radar system.
But even so, the Filter Room itself was only a part of the Air Defence Control System that was put in place. And the Ilmavoimat’s Air Defence Control System was, by late 1939 and the start of the Winter War, state of of the art and probably the best in the world, operationally at least on a par with the RAF’s (and given the superiority of “Kotkansilmissä” over the RAF’s Chain Home network, likely better overall). Illustrated below is the Ilmavoimat’s National Air Defence Centre at Mikkeli. This was constructed rapidly over summer 1939, incorporating the latest developments in Ilmavoimat monitoring and control procedures and equipment. The control centre consisted of a large concrete bunker with integral machine and plant rooms, a telephone exchange, telephone equipment room and an operations room with intercept cabins in raised galleries around the reporting room floor. Personnel working in the Centre included 'Plotters', 'Filterers' and 'Controllers'. Designed with the assistance of the noted Finnish architect, Alvar Aalto, the Mikkeli National Air Defence Centre was both futuristic looking and highly functional, designed around the filtering and flow of information with which to control the air war. Each Sector Air Defence Centre controlled its own area and they were manned 24 hours a day through out the entire war period as was the Mikkeli National Air Defence Centre where the entire air battle situation was monitored and from which overall direction was given to the individual sectors.
The Alvar Aalto-designed reporting room at the Mikkeli National Air Defence Centre . The general situations map (left) is replicatewd in Sector operations maps. It displays all information received from the Observer Corps and the Filter Room. The nationall situation map indicates positions of all aircraft, both Ilmavoimat and Soviet. The room is overlooked by three cabins with angled windows where the officers or the decision-makers sat (the Chief Controller, Fighter Controller and Anti Aircraft Liaison Officer & Searchlight Controller). The map table with its real time display provided a snapshot of events, giving the decision-makers the information they needed to bring their fighters into the battle.
The reporting room had two horizontal plotting tables with a vertical 'Tote' board detailing the status of flights and raids which could be viewed from the elevated controller's cabin. Seven plotting tables at Mikkeli showed the regional situations, the one in the illustrations above and below gave a view of the national picture.
Mikkeli National Air Defence Centre Operations Room –photo taken shortly after the start of the Winter War.
Reports from radar stations and observers would be called in by phone. By combining overlapping reports from adjacent radar stations and observers and then collating and correcting this information, accurate details of incoming or outgoing aircraft could be obtained. This process was called “filtering” and took place in Sector Filter Rooms each of which was attached to an Ilmavoimat Fighter Group. 'Filterers' received radar, visual observation and pilot sighting information by telephone and radio, aggregated this information in real time and piped the information through to the Ilmavoimat Lotta Plotters in the reporting room wearing headsets. Personnel in the Filter Rooms predominantly consisted of young women who worked in eight hour watches in the underground bunkers. To avoid errors and delays, clear Finnish was insisted upon. The Controllers were almost all recruited from the Helsinki Stock Exchange, typically because they were accustomed to making swift decisions under extreme pressure.
The Filter Room
The Filterer’s duty “was to decide the moment when a few successive plots, with all their possible inaccuracies, might be considered as a reliable track, fit for the operations room to act on for fighter interception”. Constantly on the horns of a dilemma, the Filterer had to decide whether to pass information to the Plotter on the strength of her first guess, or to wait for another plot in the hope that it would confirm or confound her suspicions. Acting quickly gained valuable time but risked fighters taking off on false information. Waiting for more information reduced the chance of interception. It was a stressful position and one that demanded a high level of intelligence and decisiveness and an ability to make decisions quickly and accurately. Speed was of the essence since there was a shortage of fighter aircraft, trained pilots and fuel. Without radar and the speed and skill of the Filter Room personnel, the outcome of the Air Battle could have had a very different outcome for Finland.
"Must be under twenty-one years of age, with quick reactions, good at figures - and female". These were the prerequisites for members of the Lotta Svard seeking a commission as Officers working in the Filter Room. This secret section of the Ilmavoimat's Defence programme in the Winter War and WW2 has never had the recognition it deserves. Nevertheless, it was one of the greatest aids to the protection of Finland and to Ilmavoimat air operations over the whole war period.
The reason that very few people even today have heard about this is the extreme secrecy which the personnel maintained about its work and its influences. Only in recent years have the restrictions been lifted and wartime members of this close group been freed from the silence imposed upon them.
The work done by the Lotta Svard Filterer Officers of the Filter Room, the Movement Liaison Officers and the Plotters who were responsible for calculating and rectifying the position, and identifying the hundreds of tracks of hostile and friendly aircraft leaving and approaching the coasts of Finland, was vital.
It is time that their valuable contribution to the Battle in the air be recognised. The Filter Room was the nerve centre of the “Kotkansilmissä” Radar system. It received information from the many Radar stations which formed a chain of protection around our coasts. This information, due to the early primitive forms of detection equipment and the possible human error of its operators needed to be instantly corrected, co-ordinated and displayed on a huge map table of the area concerned, in a form suitable to be passed on to the Operations Rooms. Without this essential link, the Radar information at that time could not have been used.
This cleaned-up (or filtered) information we have all seen in many films where Ilmavoimat Ops room plotters move coloured arrows around a map table, using a long pole-like contraption. It always appears so peaceful and bears no relation to the hectic activity that really occurred in the Filter Room.
From this information, orders were given by the Senior Officers observing from the gallery above the Ops table, for air raid warnings to be sounded in threatened areas, fighter squadrons to be scrambled, incoming hostile aircraft be intercepted and returning bomber aircraft in difficulties monitored so air-sea rescue boats could be directed to their assistance, should they ditch. The AA gun sites and Searchlight stations also relied on this information.
Finland was divided into Air Defence Sectors and there was a Filter Room for each. These were manned twenty-four hours daily from the commencement of hostilities on the 30th November 1939 until after peace was declared in Europe. Personnel were formed into four watches. Sometimes it was impossible through illness or shortage of trained personnel to maintain this and a three-watch basis was instituted. This meant leave was impossible and other than eating, sleeping and working, there was little time left.
Personnel had two fifteen minute periods when possible during the watch for a refreshment break. The food available varied considerably. Sandwiches of raw cabbage were offered throughout the night watch for weeks on end at one particular station, almost leading to a mutiny! Working conditions were often difficult and unpleasant. Many of the centres were underground where ventilation and heating left much to be desired.
The pressure of work depended upon the amount of aircraft activity and also the region involved. Naturally the northern areas were not as busy as the Filter Rooms covering the Gulf of Finland and the Karelian Isthmus. The weather too was a key factor in the activity to be expected so meteorological advices were posted constantly.
The requirement for the Filterer Officers to have quick reactions was patently obvious. They had to sort out the correct position of the aircraft from the various overlapping Radar station plots which covered the same aircraft responses. They needed to estimate both height and number of aircraft, as well as direction from information given, having intimate knowledge of the siting of the Radar stations involved and judging their accuracy. All of this had to be done with great speed.as the aircraft themselves were constantly moving on to new positions. It was found that male Filterers, mostly well over thirty years of age and unfit for front-line service for various reasons, were far too slow during periods of intense activity and they had to be removed from the table!
For the displayed information to be of value to the Operations Room, it had to be as up-to-date as possible. This meant that in times of the greatest activity, a Filterer Officer had to estimate and display salient information on up to fifty different tracks within a minute. The mental stress and physical strain were intense under these conditions and when the personnel came off watch, tension was invariably high. Throughout the meal supplied when coming off duty, the atmosphere was almost hysterical as they gradually unwound. Quite often however tired, sleep was impossible.
The mixture of backgrounds amongst the members of the Filter Room officers was amazing. Most of the senior male officers hailed from the Helsinki Stock Market where they worked as jobbers and brokers. It was an inspiration on the part of Somersalo to choose these men for the positions as Controllers and Movement Liaison Officers. All personnel involved had to have quick reactions, good mathematical ability and be physically very energetic. The women chosen ranged from psychology or science students, young actresses, society debutantes, grammar school high flyers to daughters of famous people - novelists, painters, musicians and vicars. But they were all dedicated to their work, intelligent and articulate.
Many friendships were forged under these conditions and remain close until today. Now the strictures of secrecy have been lifted, it is surely right that their dedication should be recorded. The importance of their work in the defence of Finland against the Soviet forces together with their contribution to the successful invasion of Europe and the ultimate overthrow of Hitler's forces should be made known.
The Operations Room
In the center of the Operations Room was a real-time event gridded map table providing a visual representation of the skies above Finland. Plotters used various counters on the map table to show the location of friendly and enemy aircraft. The Lotta Plotters would plot all planes based on received information from the filter section. This gave a pinpoint position, estimated height and number of aircraft and whether Identification Friend or Foe (IFF) was indicated. Enemy planes were tracked and plotted as they took off in Soviet-controlled areas, in real-time. Each radar station was allocated a colour and position plots, numbered one to five and colour-coded, signified time received. Filterer Officers - or 'Filterers' - filtered the information and passed it on to the Plotters who updated the position of the counters and placed an arrow giving direction and position. Plotters used metal poles with magnetic tips to manipulate the arrows which were colour coded in coordination with an Ilmavoimat sector clock with 5 min colour sectors to show the most recent plot information.The information on each track was displayed on a magnetised metal plaque. Every change was reflected by the counters on the table. For example, if a raid split into several smaller raids, direction changed or number of aircraft was updated.
From the elevated cabin overlooking the Operations Room, a Controller would oversee the entire situation whilst an Allocator would allocate fighters and intercepts to individual fighter controllers, who would then control the radar interceptions. The controllers and their assistants were situated in cabins behind the controller. There would be direct phone lines to the wider air defence organisation, manned by assistants who passed on the resulting information by phone to all who needed to know, including Air Raid Warning Officers, Observer Corps, AA Artillery, Air Sea Rescue Centres and Group and Sector Operations Rooms who would then order fighter interceptions of the hostiles. Radio operators were also located on a balcony overlooking the map, and relayed instructions directly to a particular squadron, or more typically, a remotely located station relaying information to a group of aircraft. Above them were status boards, consisting of a series of lights showing the current status of a particular squadron, on the ground, in battle, returning, etc. Overall direction of the battle was directed by commanders who thus had "instant access" to a picture of the battle as a whole, with the National Air Defence Centre at Mikkeli having a view of the air situation over the entire country in real time.
Mikkeli Chief Controllers Cabin. The tote can be seen through the cabin window in the reporting room.
The decision-makers would use a second user-interface model the tote board, after the horseracing tracks ''Totalisator" board. The board indicated which squadrons in what sectors were in contact with the enemy, and those disengaging to refuel and rearm. It also indicated the operational state of readiness of squadrons held in reserve that were "available" in 30 minutes, at "readiness" in five minutes, or at "cockpit readiness" in two minutes to engage in immediate battle, as well as what was in the air. The board had dozens of electric lights that ran the full length of a wall. Beneath was the map room clock with its colour coded time intervals.
An Ilmavoimat Lotta supervisor maintained the wall mounted tote board and added additional data to the arrows such as a contact number and a classification of the contact as Hostile or Friendly. The tote board would have listed the local Ilmavoimat fighter squadrons, the aircraft available and their status. With this model decision-makers had a means to respond by determining what resources were available and how they could be deployed. They could tell from the coloured counters the time segment they were dealing with. They would then pass directives to the individual squadrons and pilots. They positioned the fighters at the required operational heights to be the most effective.
Air Defence Sector Control
Sector Control Centres were similar in layout and design to the National Air Defence Centre at Mikkeli, albeit somewhat smaller.
Radar-Lotta’s monitoring airspace over the Karelian Isthmus from the large Finnish radar station outside Viipuri
Room layout of a Sector Air Defence Control Centre
Detailed layout of equipment and personnel in the operations area of a Sector Air Defence Control Centre.
A standby generator was generally housed in an adjacent building (standby set house). The final installation had a single rotating aerial array with the transmitter and receiver housed in an underground well beneathIn order to provide communication between the controllers and the intercepting aircraft, two VHF/UHF multi-channel radio transmitter and receiver blocks were built at remote sites to stop interference and swamping of the radio signals by the radar arrays. The Centre also provided information for anti-aircraft gun sites within the area controlled by the Centre.
The experiences of a Finnish radar operator
The recruitment of radar operators was not an easy task because of the need for secrecy. Recruitment officers could not be told what the Lotta girls would be doing and were informed simply that a new secret signals unit attached to the Ilmavoimat needed women recruits with a university degree or other higher education qualification, and they were asked to refer likely candidates to the Ilmavoimat recruiting officer. Most recruitment was from within the Lotta Svard organisation, but some recruitment also took place at the universities and through personal contacts. While little detail could be given to potential recruits, the requirement that they take an oath of secrecy and be subject to very stringent security checks generally intrigued them greatly.
Operators read the screens of a Nokia NR04/39 radar (as Radar became more widely used, the previous informal ET designation was replaced with the NR designation, taken from Nokia Radiomittaus, with the 04 representing the model number and /39 the year the type first entered service
Siiri Vasström was one of those excited young recruits shortly before the start of the Winter War. A university student at the University of Helsinki with a middle class background (her father was a Doctor and a staunch member of the Suojeluskuntas, her mother and grandmothers on both sides of the family were long-time Lotta Svard members). Siiri herself had joined the Pikkulotta’s as soon as she was old enough and at 17, she had transferred to the Lotta’s. On first attending the University of Helsinki in 1938, she had transferred to the University Lotta’s and started Signals training on radio equipment. She proved adept with radio equipment and to her surprise (and excitement), in mid-1939 she was approached by a senior Signals-Lotta and asked if she would like to be part of a secret Ilmavoimat Signals Unit that was being set up. After some thought, Siiri agreed and was accepted and advised that her training would start at the beginning of the Summer Holidays. In the event, she did not return to her University studies until 1941, by which time she had been promoted to Kapteeni and commanded a Radar Station herself.
Her initial training course lasted eight weeks; the first half in Helsinki and the second in the large Radar Station that had just been constructed outside Kotka. In Helsinki, the recruits were accommodated in a Girls Boarding School which had been taken over by the military for Lotta Signals training. Of course, they met many other women undergoing Signals training and were simply accepted as a different unit within the Signals Corps and the other girls were, on the whole, were not curious about what they actually did. Like almost all Finnish girls who had attended school through the last half of the 1930’s, Siiri had undergone Military Cadet training and was more than familiar with the military. Unlike other militaries of the era, the Finnish forces wasted very little time on training in the things every recruit was expected to know. Instead, after a day of kit issue, Siiri started her Signals training with a full day lecture from Major-General Aarne Somersalo, the Commander of the Ilmavoimat and Eversti Richard Lorentz, the head of Fighter Command. “The fact that Kenraaliluutnantti Somersalo and Eversti Lorentz gave us so much of their time, and explained what we were to do and our role in the Air Defence organisation in such detail impressed and motivated us all tremendously,” she wrote in her post-war autobiographical book, “One Woman’s War” by Siiri Vasström (Gummerus, 1954).
After the first two days, training began in earnest in the actual operation and maintenance of the new Radar equipment. Training also included a one week familiarization tour of the new Air Defence Operations Centre at Mikkeli, the heart of Finnish air defence as well as a week at an actual operating Radar Station. Much discussion took place among the girls as to whether it was better to be posted to a station or to Mikkeli - not that they were given a choice! Those working in Mikkeli had an overall picture of what was happening throughout the country, whilst those at a station knew only what was showing up on their own screen. “Mikkeli girls”, by working fairly closely with Military Headquarters, were often privy to secret information about special operations, major battles, the detection of Soviet naval ships and submarines, aircraft losses, etc. Such information, being totally secret, only reached the stations long afterwards, if ever. Conversely, many station operators (but not those on the islands in the Gulf of Finland) worked close to Finland’s major cities and also had all the city amenities to draw upon during their hours of leave whilst the “Mikkeli girls” lived in an isolated outpost in an unspoiled environment, with only the forest and military headquarters on their doorstep.
Siiri Vasström was always a “station girl” and her favourite, and the station where she spent much of her time over the course of the Winter War, was on the island fortress of Suursaari. To reach it, she had to travel by train to Kotka and and then travel on a fast Patrol Boat to Suursaari. “The boys on the Patrol Boats used to like giving us girls a thrill and they would ask us up onto the bridge and then make the run at full speed, which was tremendously exciting.” At Suursaari, which was securely guarded, military passes were checked and they were driven to the Central Radar Station, which was carefully concealed and mostly underground. “It had been very rapidly built in 1939 and it was brand new and to start with, all you could smell was new paint and oil. But there was always a good clean wind of the sea and after a while you didn’t notice the paint smell at all.” On arrival at the Station the girls were met by the station commander and with him, the OC Lottas, who was not much older than the girls in her charge. They were taken to their quarters - which were shielded by a standard split pole and wire fence – which the girls promptly called the “chastity fence”! A short distance from the camp and looking rather like a large garden shed was a wood and stone hut. This was the entrance to the underground Central Radar Station which monitored the airspace around Suursaari, and at the time Siiri arrived it was equipped with one of the brand new Nokia NR02/39’s. Each of the Artillery Batteries was also equipped with its own Fire Control Radar which was shorter ranged and tracked ships rather than aircraft, and they were also assigned Lotta teams to run their Radar.
The Suursaari Central Radar Station was manned by about forty personnel, all but four of them Lotta’s (the Fire Control Radar Stations had a complement of about twenty, the difference being the rather larger complement required for the Central Radar Station’s Filter Room). The few men shared the simple recreation and eating quarters with the women and, after war broke out, also shared the Spartan underground accommodation quarters as the time taken to get from the Lotta Camp to the various Radar Stations, especially at night and in winter weather, could prove critical when all personnel were required.
Plotting tracks in the Suursaari Operations Room
At the Suursaari Central Radar Station, the radar girls went on shift in teams of four, each shift lasting four hours. While one girl watched the screen, two had various tasks to perform, including marking all the air and surface plots on a map of their area while the fourth telephoned the plots through to “Mikkeli” (there was a secure undersea cable with a radio backup link). After or before night shifts, the operators slept in a room adjoining the Plotter room. In case of need, there was always one male technical staff on duty and the one entrance to the radar station was guarded day and night by a heavily armed Infantry Section from the garrison (as was each of the Fire Control Radar Stations). No one without the proper pass and password could get into the bunker and as all personnel were known by sight to the guard sections, security was always good.
Siiri was assigned to Suursaari from mid-September 1939 and found there was little in the way of recreation. “We had time off but there wasn’t much we could do. By then Suursaari was heavily garrisoned and more artillery positions and defensive positions were being prepared all the time. I think when I got there they were just finishing off installing some of the old Battleship guns they bought from the French which gave the Russians a horrible surprise when they tried to attack us. To us girls, it seemed like the island was bristling with all sorts of artillery and AA guns and there were large areas we couldn’t walk into because of all the barbed wire and landmines. There were even tunnels dug into the rocks along the shoreline for torpedo boats to hide in until the last minute and the Ilmavoimat had cut an airstrip with underground hangers dug into the rock to hide aircraft in. The whole airstrip was camouflaged by these large nets and it could be opened up and hidden in minutes. The Maavoimat boys used to call Suursaari their “unsinkable battleship.”
When we had time off the infantry boys always liked to see us and they used to joke around and flirt with us. And of course we always got invitations to dine in at the Officers Messes, which we always enjoyed. There was a lot of rivalry between the Maavoimat, Ilmavoimat and Merivoimat Officers to invite us to their messes. Us girls all enjoyed ourselves tremendously. Of course, it all changed a few weeks later when the fighting started and so many of our friends died or were injured in the fighting. But that just made all of us even more determined to do our jobs the best we could and support our boys. And we did, we were never offline for a moment, we knew we were the Kotkansilmissä and there was no way we were going to let our boys down.”
The visible part of one of the Suursaari Fire Control radar stations. Suursaari was a critical position, strategically located to command the entry and exit of ships from Leningrad and a chokepoint in the Gulf of Finland and so was an initial focus of the Soviet Navy in the early days of the Winter War. The strength of the Suursaari defenses resulted in disastrous losses for the attacking Soviet naval forces. A British newspaper correspondent called Suursaari “The Gibralter of the Baltic” and it was as accurate a description as any.
Siiri Vasström served on Suursaari through the entire Winter War, by the end of which she had been promoted to Yliluutnantti and was the Radar Station Commander.
Kotkansilmissä - a last observation
While the early Finnish Kotkansilmissä system was able to warn of enemy aircraft approaching southern Finland and the Gulf of Finland coast, once having crossed the coastline the Lotta Svärd Ilmavalonta organisation continued to provide the only means of tracking their position until mid-1943, by which time the entire country was covered by radar surveillance. Throughout the Winter War and most of the remainder of the Second World War period, the Lotta Svärd Ilmavalonta organisation continued to complement and at times replace the defensive radar system by undertaking all inland aircraft tracking and reporting functions, while the radar and radio-monitoring systems provided a predominantly coastal and southern border-oriented, long-range tracking and reporting system. In addition, the early equipping of Finnish AA Gun Batteries with radar controlled guns (achieved by mid-1940) and the use of proximity fuses had a significant impact on the effectiveness of Finnish AA Gun fire – which had already been proved highly accurate in the first nine months of the Winter War.
In combating the Soviet Air Force over the course of the Winter War, Kotkansilmissä gave the Ilmavoimat a huge advantage – while the Soviets had a small number of their own RUS-1 radars deployed experimentally, the Soviets were not even aware of the Finnish Kotkansilmissä radar networks existence or of its capabilities – with consequent effects on Soviet aircraft losses. Indeed, with the late addition of the Island stations to the network, the Finns managed to cover a good part of the Gulf of Finland as well as the Karelian Isthmus in depth, and these were the two avenues over which most Soviet air attacks on Finland were launched. And for Ilmavoimat aircrew, thoughout the Winter War (and through WW2), there was nothing quite so reassuring as the sound of the cool calm voices of the young Lotta Svärd Controllers on the Radio offering instructions, relaying information on enemy aircraft and in the event that Ilmavoimat pilots were shot down or had to bail out, calling in Search and Rescue aircraft to recover them.
The Cavity Magnetron
While everyone except the Finns and the British were working on radar at a relatively leisurely pace, the Nokia team was pushing the technology as hard as they could but making only slow progress. Fortunately, while the work struggled forward, a pair of young Ph.D researchers at the University of Helsinki who were somewhat incidentally being coached and mentored for their thesis by Eric Tigerstedt in yet another of his roles, Vilho Räikkönen and Erkki Riipinen, had come up with a new invention that would help make radar more effective all up and down the line, and put Nokia well ahead of the both the USSR and Germany in radar for the rest of WW2.
Shorter wavelengths provided a number of advantages for radar technology, including finer resolution, a tighter beam, and greater immunity to noise. However, there was simply no technology available in 1939 to generate radio waves of sufficient energy at short wavelengths. Nokia, in collaboration with a small number of other interested parties in Finland, had set up a special team to investigate radar that would operate at ten centimeter wavelengths, in the microwave band. A Fenno Radio team was assigned to work on a microwave receiver, while a team from the physics department at the University of Helsinki was to work on a microwave transmitter. The University of Helsinki effort was led by a Swedish-Finn named Marcus Backström. Räikkönen and Riipinen were not at the heart of the transmitter development project. In the fall of 1939, they were simply trying to develop microwave detector circuits. To test their designs, they had to generate microwaves for their circuits to detect.
Every now and then people who are newcomers to a field make a great discovery, simply because they don't know what works and what doesn't. Räikkönen and Riipinen didn't know much about generating microwaves, so they set about learning how. There were two devices available at the time for the task. The first was the "magnetron", which was basically a classic vacuum diode with a magnetic field placed across it. The interaction between the external magnetic field and the electron flow through the tube produced microwaves. The other was the "klystron", much more recently invented by the brothers Sigurd and Russell Varian at Stanford University in California, and based on a "resonant cavity" through which streams of electrons flowed. Backström 's team believed the klystron was the solution for short-wavelength radar.
Räikkönen and Riipinen didn't want to spend a lot of time and effort generating microwaves for test purposes. They focused on the less sophisticated magnetron simply because it seemed simpler to work with. As they learned about the magnetron, however, they realized that they could combine features of the magnetron and the klystron and come up with something new. Working on a shoestring budget, the two men pieced together their new "cavity magnetron", as they called it. The core of the cavity magnetron was a thick copper cylinder, with a large central tunnel bored through it. Six smaller tunnels, or "resonant cavities", were bored around the central tunnel, and connected to the central tunnel through slots running down their length. The copper cylinder was positively charged, forming the "anode" of the tube. A metal conduit was inserted down the central tunnel. The conduit was negatively charged, forming the "cathode" of the tube. The cylinder assembly was sealed at the ends, and a magnetic field placed across it.
Under the combined influence of the electrical potential between anode and cathode and the magnetic field, electrons circulated in the central tunnel, producing electromagnetic radiation in the resonant cavities. The electromagnetic radiation from the cavities coupled together in the central tunnel, interacting with the electron flow to efficiently extract energy from it with high efficiency. Physicists working with the device would later describe it as a kind of "whistle", where the flow of electrons generated electromagnetic waves of a specific wavelength, just as the flow of air through a whistle generates sound waves of a specific wavelength. The frequency of a whistle is dependent on its size, with a big whistle generating a low sound and a small whistle generating a shrill one. Similarly, the frequency output of the cavity magnetron was dependent on the size of the cavities. The cavities had a diameter of 1.2 centimeters (a little under a half inch), confining the electromagnetic radiation to produce "standing waves" at 9.1 cm (3,300 MHz or 3.3 gigahertz / GHz). A tap was bored through the side of the cylinder to provide an outlet for the microwave energy generated inside.
Räikkönen and Riipinen performed the first microwave transmission using their cavity magnetron system on 21 February 1940. Within a few days, they were lighting up fluorescent tubes from some distance away, which indicated power output on the order of 500 watts. They found this unbelievable, and rechecked their figures and experimental setup. Nothing was wrong. The cavity magnetron was an entirely unexpected leap forward in microwave technology. The cavity magnetron was so promising that Backström's group abandoned their work on the klystron to work with the new device and Tigerstedt himself joined the team to work on the transmitter. Through the spring of 1940, they continually improved their crude microwave transmitter into something resembling an operational system, with a maximum output power of 15 kilowatts, three orders of magnitude greater than the output power available with any other device.
The cavity magnetron opened doors to new technological possibilities. Nokia Radar received its first cavity magnetrons on 19 July 1940. Schonland’s team quickly put together a microwave radar system operating at 9.1 centimeters, though the technology was referred to as "10 centimeter" for convenience, and tracked an aircraft with it on 12 August 1940. The next day, the radar tracked a technician riding a bicycle carrying a tin sheet. Ground "clutter" would have simply blinded any long-wavelength radar under such circumstances. Microwave radar had arrived, not quite in time for the Winter War but certainly in time for Nokia to make some giant steps ahead prior to early 1944 when Finland reentered WW2.
It should be no great surprise, given the fact that radar itself arose simultaneously in several countries, that several other nations discovered the cavity magnetron at about the same time. Two Soviet engineers, N.F. Alekseev and D.D. Malairov, developed the technology in the late 1930s and actually published a description of it in a public technical journal in 1940. The fact that it wasn't kept a secret indicates the importance, or lack of it, assigned to it, all the more so because the Soviets took secrecy to an extreme. Soviet radar design was badly hampered by bureaucratic indifference and incompetence, plus the fact that a number of first-class engineers were arbitrarily purged and sent off to forced labor camps, from which many never returned. The USSR didn't exploit the cavity magnetron until after the Western Allies had put it into extensive use, and Soviet radar designs lagged badly. They received radar gear from Britain and the US, building copies when it seemed like a good idea, as they did with GL Mark II. Postwar Soviet radar work was almost all based on technology provided by the Western Allies.
Magnetron technology was also invented roughly in parallel in Switzerland, France, and Japan. In a further irony, the Japanese design was based on a device built in the mid-1930s by an American engineer, Arthur L. Samuel of Bell Labs that he never got to work very well. Samuel did make a major contribution to early Allied longwave radar work by designing a high-frequency triode vacuum tube known as a "doorknob" for its appearance. It appears that Räikkönen and Riipinen, whose naivete in electronics was obvious, knew little or nothing of any efforts similar to their own being carried out outside of Finland. Ironically, both the Americans and the Germans had worked hard before the war to come up with a device to generate high power, short wavelength radio signals and missed the cavity magnetron, while the Finns and the British basically stumbled onto it by accident at almost the same time and both ran with it.
The cavity magnetron would be at the heart of the revolutionary new Nokia 10cm Radars, the NK08/42 which were manufactured specifically for the Finnish Navy. Their small parabolic aerials projected a very narrow radar beam which was ideal for detecting S-Boats, Submarine conning towers and sometimes even their periscopes – and they were largely instrumental in ensuring that the Finnish Navy completely dominated the Baltic Sea. Even following the end of the Winter War, the Finnish Navy refused to lift the blockade of Leningrad and maintained complete control over the Baltic north of the line Osel Island – Stockholm. Both the USSR and Germany were advised that any German or Soviet vessel identified in Finnish-controlled waters would be sunk on sight and Swedish naval vessels were permitted only with advance notification. And indeed, a number of both Soviet and German warships and submarines were sunk, almost all after the start of Barbarossa. Soviet submarines attempting to leave Leningrad for the southern Baltic were sunk and, as the Germans advanced north, German warships supporting the invasion of Estonia that transgressed the line and did not turn back were also sunk, resulting in a distinct cooling in the German attitude to Finland.
And aside from the politics, one of the factors that was uppermost in Finnish naval thinking at this time was of course the effectiveness of their NK08/42 Radar fitted on their destroyers, corvettes and the Patrol Boats that maintained Finnish dominance of the northern Baltic through the war years.
As a note of interest, today almost every home has one of these secret magnetrons - inside the microwave oven!
Next: Radar for AA Guns and for the Merivoimat
Early in 1939, with the first production air and surface surveillance sets having been completed, the Nokia R&D Team would resume work on a mobile radar system for use with AA Guns, with a second version designed and developed for Naval Fire Control.
Mobile AA Gun radar was trialed in mid 1939 and volume production started in the first quarter of 1940 after teething problems had been worked through. The system was installed on a four-wheel trailer with a theoretical distance limit of about 25 km. The angular resolution was 0.5 degrees and error in distance 25 meters.
By the spring thaw of 1940, all Finnish Navy surface warships had also been equipped with a naval version of “Kotkansilmissä”.
We will look at both of these in the next Post.
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With the success of the first Nokia Radars, Nokia was immediately asked to design, build, and test radar antenna equipment to be used with the Bofors 76mm anti-aircraft gun batteries that were the mainstay of fixed AA defences. Working under top-secret security conditions, Nokia managed to build the project ahead of schedule, and at only 44% of the estimated cost! The system was packaged in several truck and trailer loads and was by no means a mobile system. Design work began in mid-1938, and again it would appear that the Nokia effort benefitted substantially from the work completed in Germany. By October 1938, Tigerstedt had completed detailed designs (and had also spent some time with the Manager of the Ford Motor Vehicle Manufacturing Plant at Hernesaari, near Helsinki. The Ford Manager advised Tigerstedt that the paraboloid antenna could not only be made of steel, but could be stamped using auto presses; he also criticized the gearing Tigerstedt used to turn the dish, advising Tigerstedt that it was unsatisfactory on several counts, including long trains of spur gears, weight, parts non-interchangeability, and inability to achieve close accuracy.
Tigerstedt was no mechanical engineer – he asked Ford to work on the design and a small team of Ford engineers was brought in immediately. They did a complete redesign while the Nokia team continued to work on the radar receiver and transmitter design. The end result was that the system cost a mere 20% of the originally estimated per-unit cost (at 460,000 Markka per unit rather than the 2,400,000 Markka per unit originally budgeted). The Nokia team had developed an accurate system based on a klystron microwave tube operating in the range of 54 to 53 cm (553 to 566 MHz) – an extremely short wavelength for the time – with a pulse length of 2 microseconds, a peak power of 7 to 11 kW, and a PRF of 3,750 Hz. The radar used a large 7.4m paraboloid dish antenna and had a a maximum range of about 43 kilometers. Lobe switching had been added to the design to improve aiming accuracy. This was achieved by sending the signal out of one of two slightly off-centre feed horns in the middle of the antenna, the signal being switched rapidly between the two horns. Both returns were sent to an oscilloscope display, slightly delaying the signal from one of the horns. The result appeared as two closely separated "spikes" which the operator attempted to keep at the same height on the display. This system offered much faster feedback on changes in target position, and since any change in signal strength would affect both lobes equally, the operator no longer had to "hunt" for the maximum signal point. An almost identical system was used by both the United States' first gun-laying radar, the SCR-268, and the German Würzburg C Radar. Azimuth accuracy was 0.2 degress amd elevation 0.1 degrees, more than good enough for direct gun-laying.
A prototype had been built over November-December 1938, minor modifications were made after trials and production began in March 1939. One Radar unit was teamed with a heavy anti-aircraft battery of four Bofors 76mm AA Guns (the standard Finnish Heavy AA Gun by this time, built under license by Tampella), a power source and a Stromberg-built gun director. The scanning pedestal or antenna mount turned at 1,750 revolutions per minute. The system interpreted the return signal and determined direction, speed, altitude, and course of the target. Once locked on, the antenna tracked target evasive moves and synchronized the guns. The equipment was designed to cope with aircraft speeds up to 700 miles per hour, up to 60,000 feet, at a target distance of not less than eight miles. The top-secret proximity fuse which Tigerstedt had designed completed the ensemble, since it was effective if triggered within about seventy feet of the target. Gear train accuracy was fundamental to success. In a matter of months, the whole project had been taken from concept to production thanks to a small group of Finnish scientists and engineers. Nokia engineers masterminded the principal electronic features of the apparatus while Ford Finland solved pedestal mounting, dish rotation, and transportation aspects of the system.
The paraboloid reflector dish was engineered at Ford Hernesaari to be made out of steel, rather than the aluminum used in the experimental model at the Nokia Laboratory. Ford Hernesaari was asked to work out the unsolved mechanical problems of gunlaying short-wave radar, and then develop manufacturing machines, tools, processes to achieve quantity production. The AA Gun Radar required gearing that would hold to a maximum accumulated backlash of 3.375 minutes out of a total 21,600 minutes of measurement. The motor specified turned 3,600 rpm. The dish could turn a maximum of eight times per minute horizontally and less than four times per minute in elevation. Thus reductions were necessary of 472 to 1 and 1,080 to 1 respectively. So far as was known up to that time, the solution was another Ford First: a special planetary-type gear arrangement 2 and 7/16 inches thick and 6 and 7/8 inches in diameter produced a reduction to 120.8 to 1. In turn, this was made to connect with three conventional spur gears with an additional reduction of near 9 to 1, bringing total reduction to 1,080 to 1. The total reduction was completed in a smaller space than the conventional approach of using three spur gears to obtain 8 to 1 reduction. The combination of dual planet gears, in association with a fourth member, a second annulus gear, was unique as far as was known at the time. The parties involved in the project considered this engineering success one of the major contributions to the success of the antenna system.
In addition, the spinner motor required an unlubricated air seal to prevent absorption of short wave impulses by the hollow radio frequency transmission lines. The seal held six pounds of pressure, provided by a small compressor. Friction was minimized by use of a special Ford finishing process, yielding 95 percent optically-flat surfaces on the bellows and seal. The carbon disc (shades of Fluid Drive) between the housing seal and sleeve was also finished in this manner. Pedestal support castings served as dimensional foundations for the whole assembly, and thus were made to extreme accuracy. All wire harnessing was color-coded to distinguish separate circuits, totally interchangeable, machine-tape-bound, and fungus/insect resistant. Ford Engineering also designed a special 19 foot, ten-ton semi-trailer to carry all the components of the Radar. By no means were these commercial trailers, since they were much stronger.
Nokia and Ford shipped unit one to the military for accelerated testing on December 4, 1938. System two was placed in the military’s hands on December 26, 1938. Two more went to the Antiaircraft Board for preliminary trials. Because of the urgent need, Ford and Nokia continued to produce while the intensive testing proceeded and completed a further five systems during the testing period through to March 1939. By August 31, 1939, 61 systems had been shipped and all existing Heavy AA Gun Batteries were equipped with the units. Production then continued at a slower pace. The production of the Stromberg-built gun directors proved to be more of a bottleneck than production of the radars (something we will cover when we turn to looking at AA Guns in detail).
A Nokia NR-I-03/39 AA Gun Radar. The operators enjoyed the comfort of a cabin. Most NR-I-03/39’s were fixed, but the radar could also be mounted on a railway wagon for a degree of mobility.
Railway-wagon mounted Nokia NR-I-03/39 AA Gun Radar. A small number of these were used in the fighting on the Karelian Isthmus, mostly in conjunction with AA defence for the large caliber Railway Guns that the Maavoimat used in limited numbers.
Nokia NR-I-03/39 AA Gun Radar prepared for railway transportation. The entire unit weighed approximately 25 tons.
Nokia NR-I-03/39 AA Gun Radar antenna dish being mounted onto both hinge frames
Nokia NR-I-03/39 AA Gun Radar Control Cabin being moved into place
The Nokia NR-I-03/39 achieved outstanding results in the Winter War. In all cases, use of the equipment to direct the hurling of a deluge of 76mm antiaircraft shells saved many Finnish lives, both civilian and military. Tampella continued to produce Bofors 76mm AA guns through the Winter War, resulting in a steady increase in the protection able to be offered to important industrial and military facilities as well as to the larger cities. The accuracy of Finnish AA Gun fire was already high – with the steadiy increasing use of the Nokia NR-I-03/39 combined with the new proximity fuses, it became lethal to Soviet aircraft to venture anywhere within the range of Finnish Heavy AA Gun batteries.
After the Winter War, Nokia continued to incorporate design improvements and work to reduce the size of the equipment whilst maintaining its effectiveness. The end result was by early 1944 a mobile unit needing only one truck and trailer to transport, capable of being erected and in use within twenty minutes.
The Nokia Mobile Radar system was a truck-mounted search radar used post-1943 by Maavimat AA Gun Batteries.
Radar for the Merivoimat
With the first Nokia Radar’s proving to be effective for air and surface surveillance from coastal stations, attention turned almost immediately to the parallel development of naval versions, one for long range detection of surface and air threats, and two further types, one specifically for naval gunnery and the other for Naval AA gun control.
Long-range surveillance was perhaps the most easily addressed – the existing radar being installed in the Kotkansilmä sites was rather rapidly navalized and designated the "NR-M/01/39." Some design modifications were made to improve performance, resulting in a maximum range against a ship-sized target at sea of up to 140 miles on a good day, though rather more typically it was only half that. Still, this was a significant improvement on visual observation and worked equally as well in darkness. A prototype set was available from the Nokia team by the end of 1938, and put through successful sea trials in early-1939. The "NR-M/01/39" sets began to be installed on Merivoimat Destroyers starting in mid-1939, following which the sets were then installed progressively on the ASW Corvettes and Icebreakers.
Finnish Grom-class Destroyer fitted with the long-range surveillance "NR-M/01/39", surface fire control "NR-M/02/39" and anti-aircraft fire control "NR-M/03/39" radars. By the summer of 1940, Finnish Destroyers fairly bristled with antennae of various sorts – 3 types of radar, radio and radio direction-finding aerials. They also bristled with AA Guns.
A substantial effort went into the development of a Radar that could be used for naval gunfire control. Designs for a production set for long-range surveillance, "NR-M/01/39", surface fire control, the "NR-M/02/39", and for anti-aircraft fire control, the "NR-M/03/39", were finalized shortly after the trials and all were in place in January 1940 and were being delivered to the Merivoimat and installed on ships starting from February 1940. All the Merivoimat radar types used "Yagi" antennas, essentially a row of dipoles of increasing size mounted on a rod, with the beam generated along the axis of the rod. The antennas, which workers also called "fishbones" for their appearance, were arranged at slightly different angles away from the centerline of the radar, with each side driven in an alternating fashion. The returns to each side would be different until the target was on the centerline. This technique, known as "lobe switching", could provide very precise azimuth angles. Both the NR-M/01/39and NR-M/02/39 had horizontal lobe-switching while the NR-M/03/39 also had vertical lobe-switching, which would was handy for an air-defense radar.
Maximum range against a ship-sized target at sea was up to 220 kilometers (140 mi) on a good day, though more typically half that. Performance was otherwise similar to the land-based system, with a range accuracy of about 50 m. This was considerably more accurate than the guns they ranged for, which typically had spreads of over 100 m. It was also much better than the optical rangefinding equipment of the era, which would typically be accurate to about 200 m at 20,000 m. As far as radar equipment for naval AA guns was concerned, it would have been impossible to adapt the early radar with its huge parabolic antenna and designed for heavy AA gun batteries for naval use on Destroyers and Corvettes. The equipment was simply to large and unwieldy. A decision was made to try and adapt the existing NR-M/03/39 for AA gun control. The new radar was designated the NR-M/03/39 and was a “Yagi” (mattress) style 2m x 4m antenna mounted in a yardarm. This radar also had lobe switching, giving it a high enough degree of accuracy to be useful for direction of AA guns, but the movement arc was limited and technicalities had not been fully though through at the time of the start of the Winter War.
The problem of retrofitting Radar equipment into Finnish warships was solved in various ways for each of the different types in servive. In the Grom-class destroyers, a new Radar cabin was generally shoe-horned in behind the bridge while the Radar mast and antenna were fitted to the existing mast. On the ASW Corvettes with their more limited space, the cabin was also located immediately behind the bridge and was a rather confined space for the equipment and personnel. Security was paramount but inconsistent in these fittings. Official photographs of the ships would have the sparsely ribbed, bird cage antenna censored from the top of the mast, whereas standard Supply Demands would have the shipment marked with the notation "for installation in the RDF cabin". Initially, each Radar-equipped ship was required to carry six additional Wireless Telegraphy (W/T) operators, two additional Wireless Telegraphy (W/T) Petty Officers and a RDF Officer, all specially trained in the use of the equipment. Radar detachments received very specialized training, including how to maintain and repair there equipment, and were also responsible for the security of the equipment. They carried sidearms, no non-detachment personnel were permitted within the Radar cabin, with the sole exceptions being the Captain and First Lieutenant of the ship. They kept very much to themselves, having little in common with the average seaman with whom they were quartered as Merivoimat security were concerned that some individuals might overhear and possibly, with careless talk, unconsciously pass on sensitive information.
Overall, Merivoimat Radar was probably the best in the world overall in late 1939, and the Merivoimat had certainly devoted time, resources and training to the effective integration of radar into maritime combat. The quality of both the equipment and the radar personnel was high. The Merivoimat’s special training facility at the Turku Naval Base which used simulated combat conditions to train naval personnel had a marked impact on the effectiveness of naval personnel in combat. Nicknamed “FNS Paniikki,” the simulator (contained within a large warehouse) combined mockups of the Bridge, Gun turrets, AA Gun positions, Engine Room, radar and radio offices and other key positions on movable platforms which could be rocked and swung to simulate conditions at sea, while movie screens portrayed simulated external views. Weather and sound conditions were also simulated, to the extent that participating personnel were often drenched in sea water and deafened by explosions, all whilst having to respond to every combination of circumstances that the training personnel could think of. Radar was quickly incorporated into the simulation and its usefulness drilled into naval officers.
Other radio-based equipment
Other radio-based equipment was also added to the warships over 1938 and 1939, all of it sharing the existing Radio and Radar cabins and all requiring additional personnel to use it. And all of it proved invaluable in the fighting to come. Aside from Radar, all Finnish warships also found themselves being fitted with modern VHF voice radios for voice communications within naval task groups and convoys (VHF radio sets for Finnish merchant ships were slowly stockpiled and personnel to used them trained – the plan was that in the event of war actually breaking out, they would be retroactively fitted into Finnish merchant ships, as indeed they were). Incidentally, a similar approach was taken to the installation of AA guns on Finnish merchant ships, with both 40mm and 20mm AA guns supposedly being stockpiled for installation on merchant ships. With this in mind, many Finnish merchant ships found gun platforms being added post October-1938 as they docked in Finland to unload and load cargo. In the event, most of the AA guns stockpiled for this purposed were actually taken over by the Maavoimat when war looked inevitable).
VHF voice radio was quickly being adopted over 1938-1939 thanks to developments in the Ilmavoimat and the tactical use of voice radio was perhaps the most important advance in wireless communications made by the Merivoimat. This explosion of voice radio reduced the amount of communication passed by flag or light signals. Erik Larsson of Turku describes some radio fittings when he joined the Merivoimat. "In 1937 when I joined the Naval Reserves, all Merivoimat destroyers were fitted with Merivoimat radio gear. When I first joined the ship, she had, in the radio office, a single tube Naval Pattern transmitter with a spark gap transmitter as a back up and a a low power transmitter and receiver for fire control purposes. All receivers were battery operated. In 1939, we got out first VHF Voice Radio which was used as a voice intercom between ships. Now, the ship had radiotelephone capability, but early in the game, only the captain or a specially designated officer was allowed to use it.”
A further piece of equipment that was also installed in 1939 was High Frequency Direction Finding (HF/DF) sets. Medium and low frequency radio signals have very long wavelengths so there is little hope of building efficient, highly directional shipboard DF antennas at these frequencies. However, at relatively short distances, even a small antenna will work because enough signal will be present for detection. Most warships of the inter-war period were fitted with direction finders whose antennas consisted of a pair of crossed loops. They were generally described as navigational in nature, but they could also be used as a means of detecting enemy transmitters “just beyond the horizon”. High frequency direction finding (HF/DF) was a relatively new development at the outbreak of hostilities in late 1938 and experience in correct operating techniques had to be gained step by painful step during the actual fighting.
The shipborne HF/DF sections were charged with the task of intercepting and reading Soviet (and later German) low-grade radiotelephone traffic. Generally speaking, operators were fluent in Russian (and later were also expected to be fluent in German). “Every large warship (in Merivoimat terms that meant Destroyers, ASW Corvettes and the ASW Patrol Boats) was provided with an HF/DF Unit for the interception and interpretation of enemy air and naval R/T on VHF. Some fifty Merivoimat warships in all were fitted with HF/DF units”.
This is the actual HF/DF Office aboard a Merivoimat Grom-class Destroyer during the Winter War. Pictured is the Nokia Model 01/39 receiver unit which was only removed in 1949 (Merivoimat photo MK-1749-49)
Antti Nikulainen of Viipuri relates his experiences as an HF/DF operator. "Being a seaman a well as having knowledge of Russian (my parents were Ingrians from Leningrad who had crossed the border to Finland shortly after the Bolshevik’s took over there), I volunteered for any job where I could be of use. Once I was drafted to a ship, I was accompanied with a special Nokia VHF radio set, plus aerial and of course a copy of the code used by the enemy. On the destroyer I was assigned to, my action station was in a small office just below and aft of the bridge. Communication with the bridge was through voice pipe. Even when not at action stations monitoring the radio, I would listen in on what was happening on the bridge. On one occasion, enemy aircraft were giving a sighting report on our position while leaving Kotka and only a short time later, we were attacked by enemy bombers! On another occasion, I picked up a transmission from an enemy submarine and the Captain used that to help find the submarine, which we later attacked with a couple of other ships. We sank the submarine, which at the time I found very satisfying. Later on I volunteered for service in the new ships we were starting to get and I ended up being assigned to one the Light Cruisers we got from the Italians, fortunately not the one that was sunk by the Germans, and stayed on that as the Section Chief right through to the end of WW2. I think the most dangerous time I had was on the Helsinki Convoy when we had to fight the Germans to get through. Overall, it was a fascinating job almost guaranteeing action – and we saw plenty of that".
From the beginning of 1939, the Merivoimat had a shore based HF/DF organization in existence. The network of stations grew rapidly over 1939 to include shore stations down the length of the Gulf of Finland and on the island fortresses. Using these HF/DF stations, cross bearings could be taken by means of all these stations and fixes were plotted by the operational filter rooms. Naval ships would then be alerted and the courses of merchant ships altered, if necessary and aircraft or naval hunter-killer anti-submarine groups could be dispatched to the area of a HF/DF fix. These HF/DF stations were normally co-located with the new radar stations that were being setup at much the same time, and informationwas fed up to the same “Filter Rooms” for operational use. The addition of more shore stations and the installation of HF/DF equipmengt eventually produced a system that was amazingly accurate, particularly in identifying Soviet submarine transmissions in the Spring and Summer of 1940, when the Soviet Navy attempted unrestricted submarine warfare in the Baltic. Between using Radar and HF/DF, fixes could be quickly obtained on enemy units and then broadcast to the ASW warships at sea.
Mikael Laine of Kotka was an Anti-Submarine Warfare Officer with the Merivoimat during World War II. He gives a glimpse into the methods used to report the vicinity of Soviet (and later German) submarines. "From 1939 on, we had the Gulf of Finland and the Gulf of Bothnia lined with a network of radio direction finding stations. Later on, we established some more or less secret stations along the Swedish coast with the cooperation of the Swedish military, although I’m not sure if the Swedish government ever knew what was actually going on. Using direction finding antennas, we monitored the Soviet submarine 'reporting' frequencies. The operators copied exactly what they heard and immediately relayed that information along with date, time, frequency and bearing to a central collection point (the “Filter Room” for the naval war). This data was compared and analyzed and an approximate position of the transmission was determined and then a report was sent out immediately giving the estimated time and position of the submarine which had made identifiable transmissions. It was all submarines in 1940, after we took care of the Soviet surface fleet in December 1939. The system worked very well and was aided by the fact that the Soviets never changed frequency over the entire length of the war. We had different problems on the Atlantic Convoys to the US and on the Convoys to Britain, especially after the Germans occupied most of Norway. That was pretty tense, and we had to fight the German U-boats off, and that was a different story, I can tell you that!”
A preliminary mention of the Atlantic Theatre
The elimination of the Soviet surface Navy in the Baltic was achieved early on in the Winter War, after which the main threat was from Soviet submarines. The Merivoimat had been heavily augmented in September 1939 by the surviving Polish warships and submarines which had withdrawn to Finland (or in two cases out of the Baltic completely to Norway where they joined the Merivoimat warships based out of Lyngenfjiord). Merivoimat ASW warfare in the Baltic was particularly successful, and from Spring 1940 on submarines were not a serious threat to Finnish merchant shipping carrying cargo from Finland to Germany (a trade which continued right up until April 1944 for reasons of pure economic necessity on both sides, given that after the Helsinki Convoy of Spring 1940 there was very little love lost between the two countries). However, the Atlantic was a different story. Immediately after the outbreak of the Winter War, with access through the Baltic largely cut off, Finnish imports and exports were conducted through the Norwegian ports of Narvik and the newly constructed port of Lyngenfjiord. However, Finnish merchant shipping to and from the USA, Britain and France (and anywhere else for that matter) was at risk of attack from German U-boats which were then beginning to attack merchant ships bound for Britain.
The Merivoimat was quick to react to this threat, assigning a small number of their ASW Corvettes to operate from Lyngenfjiord, escorting convoys of Finnish merchant ships. With a very limited number of warships, the defense that could be offered was limited to start with. However, the situation improved somewhat with the two Polish destroyers arriving and them some more as the Merivoimat pressed into service two Soviet destroyers captured in a relatively undamaged condition in Murmansk. Finland had also placed orders for the construction of a small number of ASW Corvettes with a US shipyard and these were delivered impressively quickly towards the end of the Winter War, although unarmed. For Finland (although not for Norway), the situation improved further still after the German invasion of Norway, when the Finns “took over” two Norwegian Sleipner-class Destroyers that had withdrawn North in the face of the German attacks – an event which had led to Finland seizing the Finnmark, although not Narvik. After the events of the Helsinki Convoy and the Battle of Bornholm, an unmitigated disaster for the Kriegsmarine, the Germans had wisely decided to let well enough alone and had not challenged the Finnish occupation of the Finnmark, although the level of tension along the demarcation line and in the Baltic was always high.
However, this applied only in northern Norway and did nothing to stop German U-boats attacking Finnish merchant shipping in the Atlantic. A number of Finnish merchant ships were lost before the Merivoimat instituted its own convoy procedures, initially protecting Finnish ships between Lyngenfjiord and Iceland. With four ASW Corvettes, two (reflagged) Polish destroyers, the two reflagged Norwegian destroyers and the two captured Soviet destroyers, the Merivoimat could offer only a minimal level of protection.
Polish Grom-class Destroyer heading for Narvik and refuge: late September 1939
This was soon enough augmented by the conversion of twenty three Norwegian whaling boats to Convoy Escorts. Large numbers of Norwegian whalers had been laid up in Narvik and the Lofoten islands as a result of the war at sea. They were fast enough, and very seaworthy with a long range. But they were small for a warship and the armament that could be fitted was limited – generally all they carried was a light gun, usually a Tampella manufactured Bofors 76mm naval gun, fitted forward of the bridge, a couple of twin-20mm’s either side on the wings above the bridge and a Bofors 40mm AA gun immediately aft the funnel. All the stern deckspace was taken up with twin depth charge launchers and depth charges. After the guns and additional equipment such as the Radars, Radios and Asdic was fitted in, there just wasn’t that much room. The crews were far larger than they were intended for and conditions were incredibly uncomfortable, especially in winter, but the men were seamen and all volunteers – many of them the Norwegians who had originally crewed the ships – and they were all keen to join the fight one way or another.
After reaching an agreement with the Norwegian-government-in-exile, approximately twenty three Norwegian whale-chasers that were considered large enough and suitable for the work were hastily converted by the Merivoimat to ASW escorts. With the exception of their depth charges, they were lightly armed but they were fast, maneouverable, and they served to augment the larger Destroyers and ASW Corvettes in convoy escort work.
And to protect their convoys, the Merivoimat instituted some of the same techniques they had used against the Soviets in the Baltic, setting up HF/DF stations on the Norwegian coast and in Iceland. This was helped by the more frequent radio transmissions made by the German U-boats.
A Merivoimat HF/DF operator would listen on an assigned frequency. These frequencies were listed in numbered sets called a Series. Two examples of these frequencies were 10525 and 12215 kc. U-boats would generally make brief radio transmissions at regular intervals. On hearing a U-boat transmission, the intercepting operator would press a foot pedal which activated a microphone. He would then shout a coded warning to other HF/DF equipped ships to tune the intercepted frequency. After the other escorts obtained bearings, the results would be passed to the Senior Officer (SO) of the escort group and a fix obtained where possible. If it was within an estimated 15 to 20 mile radius of the convoy, the Senior Officer would send an escort chasing down the bearing. The SO would also have a message transmitted notifying the (British) shore authorities of the U-boat's bearing or position (unofficially, the Merivoimat gave as much assistance to the British as they could – the Germans on occasion protested, but the Finns simply shrugged and said “stop torpedoing our ships and we can start talking about it” and so, nothing changed.
Ashore, Mervoimat operators would listen and search on their Nokia receivers. When a U-boat's transmission was picked up, the operator on watch would immediately warn another operator at a remote site where the actual work of taking another bearing would be performed. All Merivoimat HF/DF operators knew how to recognize German transmissions and there was no dearth of signals. When German headquarters needed to communicate with U-boats, they repeated all broadcasts at one half to one hour intervals in case the transmissions were garbled. There was no need for the U- boat to signal receipt of a message. The Germans's liberal use of radio made it possible for the Merivoimat in Lyngenfjiord to realistically make hour-to-hour tactical decisions then transmit those decisions to Convoy Escort Commanders at sea.
The Finnish convoys themselves ran on routes well away from the usual U-boat hunting grounds where they could, but this was often not possible, and the U-boats themselves made no effort to differentiate between convoys bound for the UK, or those bound for Lygnefjiord. But the story of Finland’s Atlantic Convoys is for another day…
Next Post: Verenimijä
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In an earlier Post, we looked at the work that Tigerstedt had put in to the “Suuritehotaisteluvalonheitin” Device. You may recall that in early 1938 the Maavoimat had established an experimental Regimental Combat Group, made up of one Armoured Battalion equipped with the 45 Matilda I’s and a like number of the Skoda TNHP tanks (which had been ordered in 1936 and delivered in 1937). The Matilda I’s were equipped with a special turret fitted with the Suuritehotaisteluvalonheitin or Combat Light, a searchlight that flickered rapidly to disorient enemy soldiers. However, as more experience was gained with this device, it had become clear that some of the earlier claims were exaggerated. It had already been pointed out that the scheme for using the triangles of darkness to cover the approach of assault troops necessitated using Suuritehotaisteluvalonheitin-equipped tanks for flank protection. It was found too, that the blinding effect was not as great as originally thought. Moreover, the whole device depended on the maintenance of secrecy untill it first used as it was realised that antidotes could be rapidly improvised and the value of the Suuritehotaisteluvalonheitin correspondingly reduced. An even more serious setback was the discovery that the use of a green sunfilter enabled an observer to see clearly the actual slot through which the light passed.
This information was communicated to Tigerstedt, and resulted in a re-think of the Suuritehotaisteluvalonheitin approach as it was becoming obvious that this could easily be countered. Now you may also recall that Tigerstedt had assisted the British inventor Baird in his work with his “Noctovision” apparatus – and that a considerable chunk of Tigerstedt’s own capital had been made from his company manufacturing infrared film and camera filters. Tigerstedt obviously made a connection between his earlier work on infrared technology and military applications at this time, although again there is no documentation to support this. However, it was at this stage that Tigerstedt experimented with the fitting of an infrared filter to the Suuritehotaisteluvalonheitin turret, creating what was for all intents and purposes an “invisible” searchlight with a constant beam. Night was turned to day – but only if you were looking through a passive infrared viewing device. And once more with the support of the military, this is what Tigerstedt turned his hand to designing and developing. And he did this in conjunction with his work on Radar, on the design of proximity fuses and on his experimental work on the use of radar to guide bombs to their target (something which was not achieved until towards the end of WW2 as it happened).
Tigerstedt’s Helsinki Laboratory in which he carried out much of his research.
The first practical commercial night vision device offered on the market was developed by Dr. Vladimir K. Zworykin working for the Radio Corporation of America and was intended for civilian use. It was not a success due to its size and cost but had been publicised in the March 1936 issue of Popular Science – and Tigerstedt was certainly aware of the work that had been done. In Germany, AEG had also started working on infrared devices in 1935 and again, Tigerstedt with his widespread contacts in the German scientific community was in a position to glean information on the research and work that had been done. In addition of course, there was also Baird’s Noctovision apparatus with which Tigerstedt was intimately familiar. All in all then, Tigerstedt was starting his work with a firm grasp of both the theory and the current state of the art technology in the field.
Within weeks Tigerstedt had design and built a prototype viewer for use in conjunction with the infrared searchlight. In the initial trial this was fitted in the Commander’s cupola but of course this meant the Driver was driving blind. A second unit was fitted for the driver of the Matilda but at this point the Skoda TNHP tank crew involved in the trial pointed out that to fight, they too needed viewers and it would be better if they head infrared searchlights that they could control. At this point, with the devices viability confirmed, a working group of Officers, NCO’s and men from the experimental Regimental Combat Group were brought together for what we would now term a “brainstorming session.” It was remarkably effective and after a solid week of discussions, the group made a series of recommendations to Tigerstedt. Chief among these were that the Skoda TNHP tanks be fitted with their own infrared searchlights and viewers to enable then to fight independently and effectively as tanks, while the more powerful searchlights on the Matilda’s should be used to support the Infantry units. In turn, the Infantry should themselves be equipped with infrared lights and viewers mounted on their Rifles and Machineguns, enabling them to fight effectively at night in conjunction with the tanks.
Tigerstedt buckled down to the task, designing and building infrared searchlights and viewers to be fitted and used for the Skoda TNHP tanks. From the sole prototype example remaining in the Helsinki Military Museum, we know that the early viewing devices are largely based on Dr. Vladimir K. Zworykin’s viewers as built for the Radio Corporation of America. However, Tigerstedt made numerous changes and improvements and the unit as it went into production showed significant differences. One unit was designated for use by the driver, one for the gunner and an external cupola-mounted unit for the tank commander by way of a mount installed in the commander’s hatchway. Initial range of the lights was approximately 100m (as compared to an effective range of 1km for the Matilda-mounted Infrared Searchlights).
The Commander’s Infrared Searchlight and Viewer. The 100m range was inadequate and while Tigerstedt struggled to come up with a more powerful light, operationally a Matilda I Searchlight Tank was attached to each troop of 4 Skoda TNHP tanks, extending the effectiveness of the Infrared Viewer out to almost 1km. By late 1939 a more powerful searchlight had been fitted giving a range of around 600m.
A battery stand and electric generator for the Infrared Lights and Viewers was mounted in the right rear of the crew compartment. An external armoured stowage bin was fitted to the rear of the turret to carry auxiliary equipment.
The units were easy to install and remove, taking no more than a couple of minutes and following further trials over the summer of 1938, the devices were put into production. By Spring 1939, all 45 Skoda TNHP tanks had been fitted with the devices.
The Maavoimat’s Skoda-built CKD/Praga TNHP Tank. Armed with a Bofors 37mm gun and 2 machineguns, with a Crew of 4 and a speed of 42kph, this was a capable armoured fighting vehicle for 1939. Fitted with Infrared Searchlights and Viewers and operating in conjunction with Infantry equipped with personal infrared lights and viewers attached to their rifles, it gave the Maavoimat a night-fighting capability that was hitherto unheard of. Later in WW2, Infrared Searchlights and Viewers would be fitted to almost all Maavoimat armoured fighting vehicles.
Tigerstedt turned next to the development of an active infrared device for the infantry. The system as developed consisted of a small infrared spotlight with a 5-inch deameter lamp powered with a 35 watt bulb (actually a conventional tungsten light source shining through a filter permitting only infrared light. It operated in the upper infrared (light) spectrum rather than in the lower infrared (heat) spectrum and therefore was not sensitive to body heat), one component of its active infrared system which weighed about 5lbs, fixed atop the Maavoimat’s impressive Lahti-Saloranta 7.62mm assault rifle. Below this infrared light was a viewer about 14 inches long that could detect the light emitted by the IR lamp. Since this light was invisible to anyone not equipped with a viewer system it gave a massive edge over relying on flashlights and flares for illumination. However, the soldier using the equipment did have to be looking through the Viewer to see anything. The maximum ramge was about 100 meters. The system mounted on the gun was linked by insulated wire to a heavy 13.5 kilogram (about 30 lbs.) wooden cased battery pack and simple control box that the soldier wore in place of his normal gear. A second battery was fitted inside a gas mask container to power the image converter. This was all strapped to a standard Maavoimat pack frame. Think of it as a very crude analog to today's night fighting systems – able to transform a normal soldier into one capable of fighting in complete darkness without revealing his position.
Here being examined by a Polish Soldier fighting with the Maavoimat in daylight, the Maavoimat’s Infrared System for Rifles was compact and advanced, certainly in late 1939 there was nothing to equal it in use anywhere in the world and it gave the Maavoimat an unqualled night-fighting capability.
Maavoimat soldier with an Infrared equipped Rifle. After trials and some very enthusiastic feedback, the system was designated “Kollikissa” and placed in production in early 1939.
Following trials in the last quarter of 1938, the Kollikissa unit was placed in production and a sufficient quantity to equip the two Infantry Battalions that were the Jaeger infantry component of the experimental Regimental Combat Group. These were largely delivered by mid-1939 and in a series of training exercises the Regimental Combat Group honed their night-fighting tactics. Weeks before the start of the Winter War, the Regiment was permitted to design their own unit patch and nickname.
It was a name that would terrify anyone the Maavoimat fought over the next 6 years. “Verenimijä”
Other Maavoimat units would go on to utilize the Kollikissa units, with Night-Sniper units forming a part of almost all Maavoimat Infantry Battalions before the end of the Winter War. But it was “Verenimijä” that would conduct large scale night attacks throughout the war, often eliminating enture Soviet battalions in sudden attacks in the darkness of the night. They would become the most feared unit of the Winter War. And just the sight of their calling card, a printed unit patch, would terrify the troops facing them, who knew that death was lurking near them at any moment as darkness fell.
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The Eleventh was the British Armoured Division component of the British units that Churchill insisted be sent to fight with the Maavoimat from April 1944 (the other “British” units sent to Finland were the 15th Scottish Infantry Division, the 1st Airborne Division, the 2nd New Zealand Infantry Division, the Australian 10th (Infantry) Division, the 3rd Canadian Infantry Divison and the 2nd Canadian Armoured Brigade. In addition to the 2 Polish Divisions that were already a part of the Maavoimat from November 1939 on, the Polish 1st Armoured Division, 3rd Carpathian Infantry Division, the 4th Infantry Division, 5th Kresowa Infantry Division, and the Polish Independent Parachute Brigade were all sent to Finland on the insistence of the Polish Government-in-Exile. In addition the US reluctantly allocated the 13th Airborne Division and the 66th Infantry Division.
Both British and American commanders viewed the sending of a considerable number of Divisions to Finland as a diversion of strength from what they regarded as “the main effort.” However, the Polish Government-in-Exile insisted that all available units be sent to fight alongside the Finns, and the New Zealand, Australian and Canadian governments also insisted on sending Divisional strength units. Eisenhower worked around the political directives by sending his newest and most inexperienced Divisions, while the British General Staff were overruled by Churchill, who insisted on a strong British contribution. The end result was that by late 1943, the best part of 12 Allied Divisions were in Finland and being trained in winter warfare by the Maavoimat. It was an experience none of them would ever forget. By July 1945, these Divisions along with their 30 Finnish, 2 Swedish, 1 Norwegian, 2 Estonian, 1 Latvian and 1 Lithuanian Division comrades would be perhaps the most effective and lethal fighting force in the world. In 1945 they would also joined by the roughly 400,000 men of the Polish Home Army.
Anyhow, that’s more of an aside at this point. Right now, we’ll return to Alec Lynton-Cole’s account, which gives perhaps the only "outsiders" glimpse of the Maavoimat’s “Verenimijä” Regimental Combat Group ever documented.
“As I recall, it was early March 1944 and we had moved from a training ground in the forest north of Tampere down to near the Gulf of Finland, where we would embark on our landing craft for the Invasion of Estonia. We were based outside an idyllic little town by a lake and surrounded by immense pine forests that we trained in. Usually we were out on exercises all week, with the weekends off for a bit of R&R, which we usually spent in camp because only a few of us were allowed out at a time. There were around 45 Divisions positioned near the coast and it was pretty busy. We were being trained by the Finns, and it was like nothing we’d ever gone through before. I’d thought British Army training was tough but it was like playing in the park compared to what the Maavoimat had put us through over that winter. By now, we were realizing just how much we had learnt and we felt sorry for our friends back in the UK getting ready for the Invasion who hadn't benefitted from the training we'd received. We were reallu just beginning to realise we were mere "babes in the woods" at this sort of thing.
That week we were out on an exercise, practicing small unit tactics with our tanks and attached infantry. At the end of the third day we lagered up in place prepatory to the next day’s exercise, a river crossing as I recall, when one of the tank sentries reported a Finnish officer outside, who was insisting on talking to an Officer in the Divisional Headquarters. When the CO sent me out to see what it was all about, he told me his Battalion, from Regimental Battle Group “Verenimijä” (which was how the Finns fought, their Divisions were purely for logistical support and admin, the fighting was all done by Combined Arms Regimental Battle Groups, an approach which all of us attached to the Maavoimat adopted – usually “informally” and certainly without the approval for the Head Office “wallahs” back in Blighty) had been assigned to do some training with us for a few days. That was how it all began. At the time, I had no idea what “Verenimijä” meant, it was just one of those tongue-twistingly hard Finnish words that we all struggled with.
Everstiluutnantti (Lieutenant Colonel) Jukka Rothovius a short, swarthy, twinkle-eyed man, about my age, massively self-assured and no wonder. He wore the Mannerheim Cross on his rather battered-looking tankers uniform, together with half a dozen other medals. “From the Winter War fighting the Russians,” he told me when I asked later. He was certainly the opposite of impeccable, and he had no time for military bullshit, much to the annoyance of our Divisional CO who was a bit of a stickler for military etiquette. Rothovius informed me that his unit had had us under surveillance for the past few days and gave me a totally accurate report of our itinerary to prove it. With a grin, Rothovius went on to explain that his Battalion – a typically Finnish mish-mash of various types of tanks, Finnish infantry in their weird body-armour (that we would all come to envy them for), even stranger armoured infantry carriers and the wild assortment of strange-looking rifles and submachine-guns that the Finns used – was a specialist night-fighting unit using equipment so secret and so effective that it represented a new era in tank warfare.
He went on to explain that his unit was supposed to give us some night-fighting training. He’d spent the Winter War fighting the Russians, “my unit, always at night, we ruled the night,” he chuckled in his rather broken English. “Come with me, you will see why.” The CO gave me the OK, looking rather despondent as he did so. “Damned Finns,” I heard him mutter as he turned away, “always showing us up.” He was an Officer of the old school, the British Army was the best in the world in his opinion but while he muttered and grumbled, he loved his men and if there was a better way to fight that would keep his men alive whilst winning the battle, he drove his men mercilessly, regardless of who the lessons came from. So I joined Rothovius in his battered old Sisu-built Jeep (which was actually far tougher and more capable than the American Jeeps – Sisu had been building them under license but in typical Finnish fashion, they’d “improved” the design). We drove for about twenty minutes along various forest paths until we were challenged by first one sentry, and fifty yards beyond, another, and yet another; the kind of security you associate with guarding the Coca Cola formula!
We ended up in the depths of the forest, in the middle of a tank leaguer, a mix of US supplied Shermans, the Maavoimat’s Stridsvagn M/38 and the Säiliönmetsästäjä S/38, a “tank destroyer” as the Finns called it. The Maavoimat’s Säiliönmetsästäjä S/38 (a tongue-twister if ever there was one) was based partially on an old pre-war Czech tank design and had been built by the Finns starting from the time of the Winter War, when they’d used the small number that they had at that time very effectively against the Russians. Since then everything about it had been improved. The engine was bigger, more reliable and more powerful. The armour was thicker and stronger and the gun was a high velocity Bofors 76mm with an armour-piercing shell that would prove to be as affective as the German 88mm. It was certainly an order of magnitude better than the 75mm our Sherman’s were fitted with.
Maavoimat Säiliönmetsästäjä S/38
In fact, as we found out later, the Finns were working round the clock to replace the 75mm guns in the Sherman’s that the Americans supplied them with with their own Bofors 76mm. Rothovius men were busy welding additional armour onto the Shermans at the time we drove in to his leaguer. “No such thing as too much armour,” he commented when I asked. “Besides, we have a few old German 88mm guns and we’ve tested them on the Shermans. Opens them up like a can of sardines. Don’t want that to happen to my men.” He smiled - or at least his mouth did, his eyes never changed. “You should have seen what they did to the Russian tanks back when we were fighting them.” After I got back and sat down with the CO, we put everyone to work doing the same thing, welding every scrap of armour we could lay our hands on to the Shermans. “The Finns have a lot more experience with this sort of thing than we do,” the CO commented somewhat unhappily as he watched. “Wonder what else we should know that they haven’t thought to tell us.”
Everyone in Rothovius’ unit looked alarmingly tough and competent, if scruffy. But that was something we’d long noticed about the Finns. On the surface, they looked scruffy, they never saluted, they called their officers and NCO’s by their first names and they seemed to do things by some kind of unspoken consensus. A gesture, a nod, a few laconic words was all it seemed to take. But they worked as a team, they were fit and tough, their tactical skills were startlingly good and the accuracy of their shooting under any conditions had to be seen to be believed. We were soon to learn that their night-fighting skills were fearsome. I sat down with Rothovius and we planned out a series of night fighting exercises over that evening. Later, after eating, Rothovius offered to take me out on a short exercise one of his Task Force’s was carrying out. “Just night driving practice,” he said, straight-faced.
We jumped into his Jeep in the pitch dark of the night and then waited for five minutes as the tank and infantry carrier vehicles rumbled and coughed and snorted into life. I somewhat absently wondered what the large black box mounted above the steering wheel was - it hadn't been there earlier when we'd driven to Rothovius' camp. And then, after a short burst of radio commands, we drove off, Rothovius at the wheel and the 76mm gun of a Stridsvagn M/38 literally ten feet behind us, the closest I have ever been to the business end of a gun barrel in motion. Don’t let anyone tell you any different - it was scary. The entire convoy was on it’s way, somehow in that five minutes the whole company had loaded into their vehicles and moved off without more than a few words being spoken. There must have been about twenty of the Stridsvagn M/38’s and perhaps thirty half-tracks and the tracked Finnish infantry carriers that we were now familiar with, and the whole lot came thundering into the Division’s leaguer in the middle of the night before forming themselves up in a field nearby with a solid ring of guard positions around them. The night had been pitch black, I had barely seen the windscreen, let alone the road and I was rather more than curious as to just how Rothovius and his tanks, half tracks and infantry carriers had rocketed through the forest without any visible lights and at speed.
Rothovius grinned. “Come for another drive,” he said, his tone rather as if he was throwing a single fish to a seal. It was a moonless night, and I was once again heading out into the countryside. Rothovius was at the wheel and my fellow officer Teddy and I were in the back of that Jeep. First Rothovius drove at a speed which dimmed-out headlights allowed. Then he switched them off and really hit the accelerator. It was so dark a night that we could barely see him in the front seat, and while he had not given the impression of being nuts, I guess you do not have to be Japanese to go kamikaze. Before we could think of some way of saving ourselves, Rothovius just as abruptly slowed down, stopped, and suggested that Teddy take the wheel and watch the road through a screen on the side of that strange box in front of the driver. Teddy did, said, 'well, I'll be damned' and proceeded to go even faster than Rothovius, to my terror. Teddy was NOT a good driver in broad daylight!
Then it was my turn, and there it was: if you looked through a rectangular screen on the box, maybe six-inches-by-four, the entire road ahead was clearly visible in a pale greenish light for perhaps fifty yards or more. That was it - the 'black searchlight,' as some garbled press reports called it many years later. Rothovius told us that every tank and vehicle in his unit was fitted with it, that the tank beam was considerably longer and had enabled them to mount numerous successful night attacks against Russian armor. I have no idea how it worked, and Rothovius never told us; the fact was that, if you threw a switch, you got that beam, which was totally invisible unless you looked through the screen. So we drove right back to the mess and had a few drinks while Rothovius explained that they would be using this special night viewing equipment to fight the Germans (and us in exercises). We learnt a lot about night-fighting techniques over the next week, although we never got to use that special Finnish equipment and I never did find out much more about it.
Although in the months ahead, I did run into Rothovius’ unit again and I learnt a bit more about the Maavoimat’s “Verenimijä” Regimental Combat Group and how they operated from supporting then a few times. They were tough men alright, going out at night in their strange body armour and camouflage and attacking the Germans with a ruthless and efficient ferocity that made them the terror of the night. They scared my men, I shudder to think what the Germans thought of them. Anyhow, after we reached Berlin, I never saw any of them again nor heard anything about their night-vision gadgets, until sometime in the 1960s, when there were press reports about night-fighting equipment of extraordinary efficacy, which British and American tanks had been using in Korea, and of which the prototype was a Finnish World War II development."
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Re the "Säiliönmetsästäjä S/38," I think I came up with that name quite a while ago and never took another look at it. Säiliön was a direct translation for "tank" and I know, it should be panssarivaunu (literally armorwagon) or just panssari. Originally, I used "Metsästäjä" for that particular model because I wanted to convey a more aggressive mindset in armoured warfare and "hunter" was a bit more go-get-em than "destroyer", which is more defensive. On that basis, "Rynnäkkövaunu" (chargewagon) sounds right. I'm going to change it going forward unless anyone has any better suggestions.
And before anyone says anything, I know 30 Finnish divisions is too many. I think I was winging it a bit there. Keep in mind that there are actually more Divisions and RCT's due to increased use of Lotta's and teenagers under 18 in rear-area and support positions. Whatever I put in is just a stab at this stage until I get to working thru the whole Maavoimat man/woman-power and unit strengths. Which I will do in as much detail as everything else here. So for now, I'll leave it as written but we can all assume that it's inaccurate and will change going forward.
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