Italian submarine strategy

Discussions on WW2 in Africa & the Mediterranean. Hosted by Andy H
Wargames
Member
Posts: 452
Joined: 12 Nov 2006, 21:11
Location: USA

Italian submarine strategy

#1

Post by Wargames » 15 Jan 2023, 22:27

Question#1: I note in 1940, Italian submarines only sank two unescorted tankers, one destroyer, and one cruiser (with an escort of apparently one destroyer) in the Mediterranean. Yet no transports to Malta were sunk or hit. I attribute this to Italian submarines being assigned to stations they were not to leave, then listen, and report. These boats could hear British shipping but not get in an attack position due to distance while submerged. The strategy here being to use them to supplement aircraft recon. I find about 5 submarines were held in reserve in Italy should a convoy be spotted bound for Malta. These 5 submarines would then be sent to Malta but accomplish nothing as the convoy would arrive at night. Is this correct? Or were Italian submarines on the offensive in 1940? If so, why did they fail?

Question #2: The Italians lost five Mediterranean submarines in the first 20 days of the war (Provana, Diamante, Rubino, Vebbi Seebolli, and Argonauta. The last three on the same day.). Yet then lost NONE in July, one in August, and one in September. What caused the June losses? What were the Italians doing differently afterwards to avoid the losses of June being repeated?

Question #3: In October, Italy lost five submarines again, then none in November, and only one in December. What happened in October? And why wasn't it repeated in November/December?

Thank you! :D

Platon Alexiades
Member
Posts: 42
Joined: 10 Feb 2005, 00:54
Location: Montreal, Canada

Re: Italian submarine strategy

#2

Post by Platon Alexiades » 28 Jan 2023, 21:49

Hello Wargames,

Question #1:

Your data is not quite correct. In 1940, Italian submarines sank in the Mediterranean two light cruisers, one destroyer, one submarine, two unescorted tankers and three freighters. A cruiser was also damaged.

Traffic to Malta was rare and there were no standing patrols in this area. Malta convoys were usually made of fast ships and were heavily escorted, making an interception difficult. You are quite correct when you mention that they could hear British shipping but often could not get into an attacking position. When Italy declared war, there were some 60 submarines at sea, on patrol or proceeding their assigned area (including four in the Red Sea and one proceeding to the Atlantic).

By the end of the month, they had sunk in the Mediterranean one cruiser, one tanker and one freighter (plus a tanker in the Red Sea) but ten submarines had been lost (four in the Red Sea). This came as a great shock to MARICOSOM (the Italian Submarine Command) and it came to the conclusion that the Mediterranean Theatre was not favourable to submarine operations. It was clear that a large deployment could not be maintained as attrition at this rate would have eliminated the submarine force by the end of the year. In the next months, an average of about 18 submarines were at sea on a given day in the Mediterranean Theatre (or about one third of the initial deployment).

There were a number of reasons for the disappointing performance: clear waters of the Middle Sea meant that a submarine could be spotted from the air, some time at a depth of 40 metres. The enemy had sophisticated detection devices (ASDIC) and more effective A/S measures, slow diving speed of the submarines (60-120 seconds), noisy engines, etc. Short patrols (average was less then 10 days). Fuel economy must have been a consideration although I could not find any direct reference to it, but fuel consumption was carefully reported for each patrol. Italian industries could not supply 533mm torpedoes in sufficient quantities, submarines were modified so that usually one of the forward tubes and one stern tube had reduction rings to use 450mm torpedoes (which had no production problem and were much cheaper to produce) and torpedo salvoes were not encouraged (the sinking of HMS Calypso with a single torpedo fired appeared to justify this wrong conclusion). By the 1st of July, Italian submarines operating in the Med were ordered to sail without carrying reload torpedoes (this limitation would not be applied to submarines operating in the Atlantic). Submarines on patrol were expected to listen with their hydrophones at a depth of 30 metres (where reception was better) and only came to periscope depth at certain intervals of time. Since Mediterranean acoustic conditions were not as good as the Atlantic, this also meant that detections were also less frequent.

Question #2:

The June losses were caused by surface craft (4), submarine (1), aircraft (1).
The correct name is Uebi Scebeli and the sixth submarine lost in the Med was (Console Generale Liuzzi) in June 1940.

Question #3:

There is no particular reason why five submarines were lost in October and only one in December. One was lost by friendly fire (Gemma sunk by Tricheco), the remaining four were accounted by British destroyers (Lafolè was sunk after documents were captured from Durbo revealed her position). However, winter weather was more favourable to submarines, a periscope was more difficult to spot in a rough sea. By the end of the year, the main Italian submarine effort would be carried out in the Atlantic Theatre where successes were easier to achieve than in the Mediterranean.

You might be interested to check my uboat.net pages on Italian submarines:

https://uboat.net/italian_submarines/ac ... ments.html

Best regards,

Platon Alexiades
Last edited by Platon Alexiades on 29 Jan 2023, 07:47, edited 2 times in total.


Wargames
Member
Posts: 452
Joined: 12 Nov 2006, 21:11
Location: USA

Re: Italian submarine strategy

#3

Post by Wargames » 29 Jan 2023, 03:14

For those who don't know, Platon Alexiades is probably the foremost expert living today on Italian submarines. I'm honored he replied. Thanks! Hs comment that "the sinking of HMS Calypso with a single torpedo fired appeared to justify this wrong conclusion" is very accurate.

I have 40 miles as the Italian hydrophone range for hearing a convoy and 7.5 miles for a single ship. Does this sound right?
I have cruiser Calypso sunk in 1940. What are the other two?

Some may have noticed Platon's reference to listening at 30 meters when aircraft can spot them underwater at up to 40. The result of this was that an Italian submarine often heard nearby explosions while submerged and listening. Yet the hydrophones heard no propellers. These were depth charges being dropped on them by aircraft.

Platon Alexiades
Member
Posts: 42
Joined: 10 Feb 2005, 00:54
Location: Montreal, Canada

Re: Italian submarine strategy

#4

Post by Platon Alexiades » 29 Jan 2023, 08:12

Hello Wargames,

Thank you for your kind remarks but I do not think that I qualify as an "expert" on Italian submarines. My knowledge is perhaps above average and I suspect that many in Italy are more qualified than I am.
Actually two cruisers were sunk (HMS Calypso and the Greek Helle) and a third was damaged (HMS Coventry).
As I wrote before, acoustic conditions in the Mediterranean were not optimal so hydrophone range could vary considerably. In practice, 40 miles would be exceptional even for a convoy and I do not remember a mention of such a range in a patrol report but 10-15 miles more common, and 3-10 miles for a single ship should be about right. If I find more precise information, I will forward it.
Although an aircraft could perhaps sight a submarine at a depth of up to 40 metres, it had to be directly above the submarine to do so. In reality, this was very rare. Most of the sightings by aircraft were made when the submarine was surfaced or at periscope depth.

Platon

User avatar
Urmel
Member
Posts: 4896
Joined: 25 Aug 2008, 10:34
Location: The late JBond

Re: Italian submarine strategy

#5

Post by Urmel » 29 Jan 2023, 18:11

The Italian official history is probably going to be most helpful in this regard?

I'd be very surprised if hydrophone range was anywhere near this, given that the Germans reported sonar range to be at the low end of the single-ship estimate?

https://rommelsriposte.com/2009/07/15/g ... n-vessels/
The enemy had superiority in numbers, his tanks were more heavily armoured, they had larger calibre guns with nearly twice the effective range of ours, and their telescopes were superior. 5 RTR 19/11/41

The CRUSADER Project - The Winter Battle 1941/42

Platon Alexiades
Member
Posts: 42
Joined: 10 Feb 2005, 00:54
Location: Montreal, Canada

Re: Italian submarine strategy

#6

Post by Platon Alexiades » 29 Jan 2023, 18:50

Hello Urmel,

Thank you for your comment. The link you provided is about German Sonar (S-Gerät) which had a much shorter range than passive hydrophones. The data Wargames and I are discussing is about hydrophones. Italian submarines did not have S-Gerät but a number of Italian escort vessels toward the end of 1941 began to be equipped with this version of the German sonar.

Best regards,

Platon

Wargames
Member
Posts: 452
Joined: 12 Nov 2006, 21:11
Location: USA

Re: Italian submarine strategy

#7

Post by Wargames » 29 Jan 2023, 21:24

Platon Alexiades wrote:
29 Jan 2023, 08:12

As I wrote before, acoustic conditions in the Mediterranean were not optimal so hydrophone range could vary considerably. In practice, 40 miles would be exceptional even for a convoy and I do not remember a mention of such a range in a patrol report but 10-15 miles more common, and 3-10 miles for a single ship should be about right. If I find more precise information, I will forward it.
You may be right about convoy listening range and which is why I asked for confirmation.
The US sold its hydrophone overseas in 1931 which could hear a submarine at 3 miles. I would expect Italy, like Japan, bought it. I noted Italian boats stationed on a line 15-20 miles apart more than once and "guessed" their hydrophone range was half the distance between them or 7.5 miles (transports) and 10 miles (destroyers). I arrived at 40 miles for a convoy when I read hydrophone ranges were 40-50 miles for convoys, then found two Italian boats 80 miles apart looking for a French convoy and so assumed 40 miles range between them. The 40-50 mile source didn't say but it might have been referring to German hydrophones, then the best in the world.

Your estimate of 10-15 miles for a convoy would seem to make Italian submarines pretty useless south of Crete.
The size of Italian submarine patrol "squares" might provide a clue. Do you know their size?

Platon Alexiades
Member
Posts: 42
Joined: 10 Feb 2005, 00:54
Location: Montreal, Canada

Re: Italian submarine strategy

#8

Post by Platon Alexiades » 29 Jan 2023, 22:47

Hello Wargames,

The Italian Grid in use in the Mediterranean was divided in 20 minutes x 20 minutes squares and divided in six sub squares (each 6'40" latitude x 10' longitude). By contrast the Atlantic grid was divided 1 degree x 1 degree squares and divided in 36 sub squares (10' x 10' each). Latitude and Longitude were represented each by a pair of letters. Contrary to the German grid, the Italian one was changed frequently but at irregular intervals. If you live in the USA and have a chance to visit the National Archives in Maryland, you can check there some of the Italian grid charts pinched during the war.

Best regards,

Platon

Wargames
Member
Posts: 452
Joined: 12 Nov 2006, 21:11
Location: USA

Re: Italian submarine strategy

#9

Post by Wargames » 30 Jan 2023, 00:07

For lurkers, a 20 minute square is 18x18 miles. A submarine in the middle would be responsible for 9 miles to each side of itself. A submerged submarine can see masts at 7 miles by periscope. This suggests a 9 mile hydrophone range for hearing a single ship. 9 miles comes within my 3 mile estimate for submarines and 7.5-10 mile range estimate for freighters/destroyers. The table below, given for a submerged submarine at 4 knots, gives pretty much the same numbers:

- for a destroyer- 5 to 10 nautical miles,
- for a cargo ship- 3.5 to 7.5 nautical miles,
- for a convoy- up to 50 nautical miles.

https://uboat.net/articles/id/52

That comes from a U-boat site which used the best hydrophones. It doesn't say it's for U-boats though. One possible explanation is that Atlantic convoys numbered 45-60 ships versus 4 TR + escort in the Mediterranean. Thus, Atlantic convoys made nearly 10 times as much noise. Using 4 TR, 4 DD, and 2 A/A cruisers as a Mediterranean convoy of 10 ships, the hydrophone range would be 11 miles which compares to Platon's estimate of 10-15 miles.

If that's the case, Italy had a serious submarine patrol problem off Crete. I can't find any maps of Alexandria to Malta convoy routes except for the summer of 1942. Did they all take the same route? If not, you'd need submarines out all over the place to then be used as targets for Sunderlands and British destroyer anti-submarine sweeps.

Perhaps Platon can tell us where the Italian Crete search lines were in 1940, 1941, and 1942? And how many boats they included?

User avatar
Urmel
Member
Posts: 4896
Joined: 25 Aug 2008, 10:34
Location: The late JBond

Re: Italian submarine strategy

#10

Post by Urmel » 30 Jan 2023, 00:30

Platon Alexiades wrote:
29 Jan 2023, 18:50
Hello Urmel,

Thank you for your comment. The link you provided is about German Sonar (S-Gerät) which had a much shorter range than passive hydrophones. The data Wargames and I are discussing is about hydrophones. Italian submarines did not have S-Gerät but a number of Italian escort vessels toward the end of 1941 began to be equipped with this version of the German sonar.

Best regards,

Platon
I understand that, but wanted to note that there is no indication of the targets being picked up by hydrophone at longer ranges, and in one case a clear remark is made that the target had not been picked up at all.
The enemy had superiority in numbers, his tanks were more heavily armoured, they had larger calibre guns with nearly twice the effective range of ours, and their telescopes were superior. 5 RTR 19/11/41

The CRUSADER Project - The Winter Battle 1941/42

Platon Alexiades
Member
Posts: 42
Joined: 10 Feb 2005, 00:54
Location: Montreal, Canada

Re: Italian submarine strategy

#11

Post by Platon Alexiades » 20 Feb 2023, 23:00

Hello Wargames and Urmel,

Regarding Italian Crete search lines: there were no specific search lines and Italian submarines rarely occupied the same area twice. Most patrols were carried out by Portolago (Leros) based submarines. There were rarely more than two submarines at sea off Crete at any given time. Usually patrol areas were roughly along the 34° N parallel, anywhere between the 23°- 26°E meridians, that is mid-way between Crete and North Africa. Some patrols were also carried out in the Kaso Straits to intercept British expeditionary force convoys to Greece in 1940-1941.

Italian submarines seldom recorded in their patrol reports the range recorded by a hydrophone contact. However, I did see one instance when a 20,000 metres range was recorded. It is quite possible that contacts were made at longer range. Reviewing the poor performance of June-July 1940, MARICOSOM (Italian submarine command) noted that 225 hydrophone contacts were made by submarines (no range given) but only 40 had resulted in a subsequent visual contact.

I hope this helps.

Platon

Wargames
Member
Posts: 452
Joined: 12 Nov 2006, 21:11
Location: USA

Re: Italian submarine strategy

#12

Post by Wargames » 21 Feb 2023, 04:18

Platon Alexiades wrote:
20 Feb 2023, 23:00
Regarding Italian Crete search lines: there were no specific search lines and Italian submarines rarely occupied the same area twice. Most patrols were carried out by Portolago (Leros) based submarines.
They had the shortest distance to go.
There were rarely more than two submarines at sea off Crete at any given time.
My calculation as well.
Usually patrol areas were roughly along the 34° N parallel, anywhere between the 23°- 26°E meridians, that is mid-way between Crete and North Africa. Some patrols were also carried out in the Kaso Straits to intercept British expeditionary force convoys to Greece in 1940-1941.
They likely passed through the Kasos Strait to reach their southern patrol.
Italian submarines seldom recorded in their patrol reports the range recorded by a hydrophone contact. However, I did see one instance when a 20,000 metres range was recorded. It is quite possible that contacts were made at longer range.
The US made its listening system available in the 30's. Japan bought it. Its performance was virtually identical to what you described. Since Italy didn't get its system from Germany, the odds are it got it from the US.

Reviewing the poor performance of June-July 1940, MARICOSOM (Italian submarine command) noted that 225 hydrophone contacts were made by submarines (no range given) but only 40 had resulted in a subsequent visual contact.
Which either means they took place at night or the contact was "over the horizon" to the submarine or both. I doubt a 20,000 meter contact would be visible or at least would be at the extreme range of visibility.

Thank you for your reply and information. :thumbsup: It was more useful to me than you realize. Did these submarines south of Crete report anything? It would seem the odds would greatly favor the British passing to Malta undetected by them unless the British steered a straight from Alexandria to Malta. I don't know if they did that in 1940 (They did it in 1942 but there were no Sm.79's in North Africa then.).

Platon Alexiades
Member
Posts: 42
Joined: 10 Feb 2005, 00:54
Location: Montreal, Canada

Re: Italian submarine strategy

#13

Post by Platon Alexiades » 21 Feb 2023, 22:09

The submarines south of Crete made relatively few enemy reports. Most of these were about enemy destroyers, very rarely convoys were detected. I think there was too much reliance on hydrophones instead of the periscopes. Most of the British convoys were detected by enemy aircraft.

Platon

Wargames
Member
Posts: 452
Joined: 12 Nov 2006, 21:11
Location: USA

Re: Italian submarine strategy

#14

Post by Wargames » 26 Feb 2023, 10:36

In trying to establish where the Italian submarines patrolled, I have obtained this information. On March 21, 1942, the submarine Mocenigo sighted Force H and the submarine Platino sighted a British convoy south of the island of Gaudo. This led to the Second Battle of Sirte. It sounds like you have access to those submarine logs. With so few submarines at sea, they must have been brilliantly positioned and I'm curious where they were to do that.

User avatar
Urmel
Member
Posts: 4896
Joined: 25 Aug 2008, 10:34
Location: The late JBond

Re: Italian submarine strategy

#15

Post by Urmel » 26 Feb 2023, 16:02

Is it this what you are after?
Screenshot 2023-02-26 at 2.01.35 PM.jpg
These maps are in the USMM OH, of which an auto-translated version can be found on archive.org - while the translation is not great, the maps are in there.
The enemy had superiority in numbers, his tanks were more heavily armoured, they had larger calibre guns with nearly twice the effective range of ours, and their telescopes were superior. 5 RTR 19/11/41

The CRUSADER Project - The Winter Battle 1941/42

Post Reply

Return to “WW2 in Africa & the Mediterranean”