KM S-boat fleet ready at start of WWII?

[thaddeus_c]

what if a larger S-boat fleet was ready at start of WWII? http://german-navy.de/kriegsmarine/ship ... index.html

something around 3 - 4 times the OTL numbers? or 50 - 70

[fredleander]

Thaddeus, as the German S-boats, like the Allied MTB's and PT's, were typical short-range vessels their use, and importance, was always somewhat restricted. As a matter of fact, in the beginning of the war the S-boats were both more numerous (than British MTB's) and more effective than their typical opponents (destroyers) in the sense that more enemy destroyers were sunk or damaged during the first year than the other way around even if, as with the German Luftwaffe and the Kriegsmerine U-boat and surface fleets, their primary targets were enemy transports rather than warships.

It seems to me that it is a litte known fact that even if the S-boats had only two torpedo tubes they routinely carried four torpedoes.

If the Kriegsmarine had 60-70 boats when the war started, and we suppose that the building program had continued with a similar priority, their fleet could have been around 80-90 boats in May 1940 when they first came properly to shots with the enemy. Unlike the German U-boats the S-boat fleet had a much better utilization due to the shorter distances to their "killing fields". In general, their operational sevicability was about 2/3 of the actual number of boats, depending on how hard the units were "pushed".

As an example, in the middle of September 1940, when Operation Sea Lion, the German invasion of Engand, was ready to be launched, the Kriegsmarine Quartermaster reported 25 S-boats operational in 3 x S-boat flotillas and 1 "Schnelle U-Jäger" flotilla. If we consider the statistics from that period it gives some idea of RN's potential problems if the S-boat numbers were tripled. Particularly when coupled with the fact that the RN was restricted (by the RN leadership) from operating in the Channel during daytime - due to the experienced efficiency of the Luftwaffe.

Fred

[thaddeus_c]

my understanding is that S-boats were not subject to any treaty restrictions?

every discussion of KM devolves into battleships vs. u-boats while there were other strategies and designs available.

my scenario would be a bit earlier start on S-boat construction and use in conjunction with a larger ship(??) , my thought would be Sperrbrecher modified with more powerful engine(s)

a "scratch fleet"

[fredleander]

my understanding is that S-boats were not subject to any treaty restrictions?

every discussion of KM devolves into battleships vs. u-boats while there were other strategies and designs available.

my scenario would be a bit earlier start on S-boat construction and use in conjunction with a larger ship(??) , my thought would be Sperrbrecher modified with more powerful engine(s)

a "scratch fleet"

The reason the Germans didn't have more S-boats than they had at the outbreak of war was not because they started production too late but the Kriegsmarine leadership's lack of interest in them. Actually, the RN and the USN "sinned" even more in this respect. A question of where to use resources. The basic S-boat construction was developed before the war.

The S-boats were usually attached to a mother-ship - tender, even if land bases were developed where possible. While the UK were their primary operational area they also fought in the Arctic Seas, The Baltics, The Black Sea and The Mediterranean. As such, it was usually a matter of "too little, too late" everywhere.

That said, due to their superior construction (largely due to their Diesel engines) the S-boats had a better operational potential than the opponents' similar units.

Fred

[fredleander]

....my scenario would be a bit earlier start on S-boat construction and use in conjunction with a larger ship(??) , my thought would be Sperrbrecher modified with more powerful engine(s) - a "scratch fleet"

Well, ref. Vice Admiral Ruge the Germans actually had a quite large "scratch fleet". Already a few months after the occupation of France the security forces of BSW (Befehlshaber Sicherheit West - or something like that) and their minesweeper force covering the French coast, counted some 500 vessels, mainly a "scratch fleet". Among them quite a few Sperrbrechern.

Fred

[thaddeus_c]

The reason the Germans didn't have more S-boats than they had at the outbreak of war was not because they started production too late but the Kriegsmarine leadership's lack of interest in them. Actually, the RN and the USN "sinned" even more in this respect. A question of where to use resources. The basic S-boat construction was developed before the war.

The S-boats were usually attached to a mother-ship - tender, even if land bases were developed where possible. While the UK were their primary operational area they also fought in the Arctic Seas, The Baltics, The Black Sea and The Mediterranean. As such, it was usually a matter of "too little, too late" everywhere.

That said, due to their superior construction (largely due to their Diesel engines) the S-boats had a better operational potential than the opponents' similar units.

yes, it seems a lot of their construction program was meant to lock in resources?

[thaddeus_c]

....my scenario would be a bit earlier start on S-boat construction and use in conjunction with a larger ship(??) , my thought would be Sperrbrecher modified with more powerful engine(s) - a "scratch fleet"

Well, ref. Vice Admiral Ruge the Germans actually had a quite large "scratch fleet". Already a few months after the occupation of France the security forces of BSW (Befehlshaber Sicherheit West - or something like that) and their minesweeper force covering the French coast, counted some 500 vessels, mainly a "scratch fleet". Among them quite a few Sperrbrechern.

the more accurate term for my scenario would be stealth fleet, although the KM, my understanding, DID have an inventory of ships available.

at least some of that inventory could have been modified with more powerful engines (beyond what their normal commercial use would require), paid for by KM. so that for instance the Sperrbrecher (well armed after the war began) could have gone ?? 20 knots??
something like that would have cased big problems for GB as the ships they pressed into service, Flower-class, were slower.

[fredleander]

[at least some of that inventory could have been modified with more powerful engines (beyond what their normal commercial use would require), paid for by KM. so that for instance the Sperrbrecher (well armed after the war began) could have gone ?? 20 knots??
something like that would have cased big problems for GB as the ships they pressed into service, Flower-class, were slower.

I'm not sure your proposal was practical. To increase the speed of, say, a 5.000-ton ship designed for a speed of 12 knots to 20 knots takes an immense increase in Engine Power. What they could have done was to increase the speed onf some of their MFP's (MarineFährPrame). Many of these were rebuilt as "artillery ships". Much like the Japanese Daihatsu Landing Craft. The German emphasis was, for a large part, on coastal escorts. As such, speed was not an important issue. Even the German "Raiders" were not overly speedy.

Powerful German Diesels were in short supply and were expensive and difficult to make. At times this limited the production and repairs on their S-boats, as well.

Fred

[thaddeus_c]

[at least some of that inventory could have been modified with more powerful engines (beyond what their normal commercial use would require), paid for by KM. so that for instance the Sperrbrecher (well armed after the war began) could have gone ?? 20 knots??
something like that would have cased big problems for GB as the ships they pressed into service, Flower-class, were slower.

I'm not sure your proposal was practical. To increase the speed of, say, a 5.000-ton ship designed for a speed of 12 knots to 20 knots takes an immense increase in Engine Power. What they could have done was to increase the speed onf some of their MFP's (MarineFährPrame). Many of these were rebuilt as "artillery ships". Much like the Japanese Daihatsu Landing Craft. The German emphasis was, for a large part, on coastal escorts. As such, speed was not an important issue. Even the German "Raiders" were not overly speedy.

Powerful German Diesels were in short supply and were expensive and difficult to make. At times this limited the production and repairs on their S-boats, as well.

my thought the entire R-boat class could have been scrapped and replaced with (modified) MFPs, just using one of the two engines employed on the R-boats (900 hp) would more than double hp on MFPs.

would not discount Sperrbrecher, they proved hard to sink. they all started as commercial ships so it might be possible to purchase engines from other countries pre-war? (not sure how to calculate increase in speed from let's say adding second 3,500 hp diesel?)

[fredleander]

...my thought the entire R-boat class could have been scrapped and replaced with (modified) MFPs, just using one of the two engines employed on the R-boats (900 hp) would more than double hp on MFPs.

I'm not sure that would have been a particularly good idea. The R-boats had their missons, and they were good at it. Not only as coastal minesweepers but, as the war continued, as escort vessels, too. During the Norwegian and Danish campaigns they (and S-boats) were used in snappy landing operations. During Operation Sealion they were planned used in both their normal minesweeper-role as well as for smoke-laying, landing advance parties and as protection against enemy MTB's infiltrating the landing areas. More than 30 boats were assigned to such duties in that operation.

An interesting thought is how the R-boats would be perceived by eventual enemy destroyers approaching the landing beach areas in the dark. With their low, similar, silhouttes they could easily be taken for S-boats, making the job easier for those units to hunt the destroyers. Later, as the RN started to try to interrupt the German ship's transports along the French coast, this happened quite often when R-boats operated in the escort role. The RN destroyers had a healthy respect for the German S-boats. The destroyers would then usually be held back, supporting their own MTB's from a distance.

The MFP's, even if quite versatile vessels, had a low speed. But, as you write, could certainly have been up-engined. But, at the cost of something else. The R-boats was a class that was well developed, in reasonable numbers, even before the war started, while the MFP's was a sort of afterthought. If the Germans had considered an invasion of England Before the war started, an MFP-type could have been available in numbers in the Fall of 1940. As it were, this happened only in the Spring of 1941, the first were commissioned in April. Instead, some were transferred to the Mediterranean for the planned invasion of Malta (Hercules) in 1942.

MFP's, with their low silhouttes and draught, would probably have been better suited in their role than the couple of dozen provisional "artillery ships", converted merchants of different sizes, which were made ready for Operation Sealion.

...would not discount Sperrbrecher, they proved hard to sink. they all started as commercial ships so it might be possible to purchase engines from other countries pre-war? (not sure how to calculate increase in speed from let's say adding second 3,500 hp diesel?)

They were hard to sink. Many were sunk and damaged by mines (which was their mission, so to speak) through the war but I cannot say that I remember any incidents where sperrbrechers were actually sunk by gunfire by destroyer-size vessels. Some must have been.

There is quite a difference between a "normal" merchant and the Sperrbrecher with its reinforced hull, built-in floating materials and extensive armaments. But, to up-engine any significant numbers of them I find unpractical. Just my opinion. The Kriegsmarine would certainly have liked to have more "Raiders" than they had, too, but they needed a large, and costly, organisation to keep them operable.

The Kriegsmarine always complained they had too few Sperrbrechers to fullfill their "normal" missions.

Fred

[thaddeus_c]

...my thought the entire R-boat class could have been scrapped and replaced with (modified) MFPs, just using one of the two engines employed on the R-boats (900 hp) would more than double hp on MFPs.

The MFP's, even if quite versatile vessels, had a low speed. But, as you write, could certainly have been up-engined. But, at the cost of something else. The R-boats was a class that was well developed, in reasonable numbers, even before the war started, while the MFP's was a sort of afterthought.

...would not discount Sperrbrecher, they proved hard to sink. they all started as commercial ships so it might be possible to purchase engines from other countries pre-war? (not sure how to calculate increase in speed from let's say adding second 3,500 hp diesel?)

They were hard to sink. Many were sunk and damaged by mines (which was their mission, so to speak) through the war but I cannot say that I remember any incidents where sperrbrechers were actually sunk by gunfire by destroyer-size vessels. Some must have been.

There is quite a difference between a "normal" merchant and the Sperrbrecher with its reinforced hull, built-in floating materials and extensive armaments. But, to up-engine any significant numbers of them I find unpractical. Just my opinion. The Kriegsmarine would certainly have liked to have more "Raiders" than they had, too, but they needed a large, and costly, organisation to keep them operable.

my rationale for not building R-boats twofold, free capacity at Lurssen for S-boats and free up supply of diesel engines. but you have more knowledge of their operations and as you state the MFPs were not being built pre-war.

(not sure the POD to have MFP-type craft built, perhaps transport of tanks? short of any possible invasion of GB)

not trying to turn Sperrbrecher into destroyers but if they, along with S-boats, menaced everything up to British destroyer sized ships it would strain RN operations. my understanding the Flower-class corvette could manage 16 knots?

so an upgrade might seem impractical but it might cause Allied side to make even more difficult upgrade, and not use inexpensive types like Flower-class.

and of course the Sperrbrecher are a covert building program pre-war.

[fredleander]

....not sure the POD to have MFP-type craft built, perhaps transport of tanks? short of any possible invasion of GB)

For the Germans (and the Italians) they became quite useful as the war developed. The Italians, after the cancellation of the Malta invasion, used them to supply their forward bases in North Africa. For the Germans they were crucial in three large withdrawals - from Sicily to the Italian mainland, from the Kuban beachhead to Crimea and from Eastern Prussia in 1944/45.

Fred

[magicdragon]

It is my understanding that the basic S Boat engines were the same type as U-Boat engines (Daimler Benz MB 501 marine diesel engines) therefore without massively increasing engine supply full-stop an expanded S Boat fleet would have a detrimental effect on U Boat building (S-Boat 3 x MB 501s; U Boat 6 x MB 501s)?

[Takao]

IIRC, the DB 501s were only fitted in the IXD1 class...only two of which were built. However, the 501s performed poorly and were soon replaced.

[thaddeus_c]

It is my understanding that the basic S Boat engines were the same type as U-Boat engines (Daimler Benz MB 501 marine diesel engines) therefore without massively increasing engine supply full-stop an expanded S Boat fleet would have a detrimental effect on U Boat building (S-Boat 3 x MB 501s; U Boat 6 x MB 501s)?

OR

diesel engine production (and research) could be expanded pre-war under Trojan Horse guise of their installation in S-boats with full intent and planning to install some of production in U-boats?