After the attack on the convoy they resurface and find out that one of the ships they torpedoed, is still afloat, even though it's burning and it's almost broken in half. It looks obviously totally crippled. In order to sink that tanker more quickly, they fire another torpedo at it.

However, the rest of the fleet already moved on, they are no longer in danger, they could just have used their deck gun. In fact, U-boats in real life preferred using deck guns against targets not armed well enough to pose them a danger, because of the limited supply of torpedoes they could carry.

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they could just have used their deck gun. In fact, U-boats in real life preferred using deck guns against targets not armed well enough to pose them a danger, because of the limited supply of torpedoes they could carry.

Yes, true, but also theres a couple of other things to consider:

The captain acknowledges that she must have been a tough ship, since she is not going down easily.

Captain: Tough old tub that. She isn't settling.

German submarines during world war two did not have the most effective sinking-by-gunfire record of the major fleets during that war (due to reasons such as having a relatively short period of 'glory' in which to enjoy surface action), with the US coming out on top, actually increasing the amount and type of guns used towards the end of the war, with the Germans almost completely giving up using them and removing them completely. The British were somewhere in the middle in their experience. Mid war the Allies enjoyed air superiority which also reduced the ability of the German submarines to use their deck guns effectively. Later in the war, Germans changed their tactics and also ran submerged during the night, this was due to Allies having radar that could detect them on the surface at night, whereas the German submarines could not detect them until it was too late.

It is likely that they used the torpedo as the gun might take too long against such a large target, even in its present state.

The other thing is that the author of the book joined the U-96 7th patrol in 1941, during which it sank one ship. So its likely some of what is in the book and the movie is made of or are composites of other events in other patrols and quite possibly U-96's own previous patrols as she had had quite an eventful period before the author joined the boat, in which case individual reasoning is lost to sheer facts.

U-96 had around 7 events that sound similar to the one portrayed in the movie, some closer than others:

11 December 1940

U-96 launched a torpedo at the Dutch merchant ship Towa, hitting her amidships. The crippled ship did not immediately sink, so at 21:30 U-96 launched a second torpedo. After the second hit, the ship still stayed afloat, so the U-boat began shelling her half an hour later, eventually sinking her.

14 dec 1940

U-96 fired at the British steamer Empire Razorbill, trying to stop her. After six rounds from her deck gun which resulted in three hits. The ship escaped.

18 dec 1940

On 18 December, U-96 encountered the Dutch motor tanker Pendrecht and attacked her with a single torpedo at 16:15. The ship was hit astern but remained afloat. The crew, which had initially abandoned the ship, was able to re-board and sail her to Rothesay escorted by a British destroyer.

10 jan 1941

encountered the un-escorted British passenger steamer Almeda Star. First torpedo was launched at 07:45, hitting the ship amidships, causing her to stop. A second torpedo hit the ship astern 20 minutes later, but still did not sink. Two more torpedoes were needed before Almeda Star sank at 13:55. All hands lost.

13 feb 1941

The tanker Arthur F. Corwin had already been hit by torpedoes from U-103, and was lagging behind the convoy. U-96 launched two more torpedoes into the burning wreck, sinking her. All hands lost.

21 Feb 1941

a Focke Wulf Condor attacked and damaged a convoy straggler, Scottish Standard, and the ship was abandoned. A day later U-96 came upon the abandoned tanker. Although there was a destroyer patrolling the area, U-96 was able to launch two torpedoes, sinking Scottish Standard.

23-24 feb wolfpack U-69, U-73, U-95, U-107, and the Italian submarine Michele Bianchi.

At 02.20 hours on 24 Feb 1941 the Sirikishna hit on the port side amidships by one torpedo from U-96 south of Iceland and was abandoned by the crew. At this point U-96 had run out of torpedoes and had to unload them from containers. At 08.36 hours, a coup de grâce was fired that hit amidships and caused the ship to sink. Although the crew abandoned ship and went in the water, there were no survivors.

Those events were all in the log book from the current commander from the first three war patrols.

  • What is notable in these events is that only twice did they use the deck gun, and that was successful only once, the rest of the time torpedoes were used. It seems that many of the ships turned out to be quite tough, perhaps too tough for the guns embarked on the submarines, hence the use of torpedoes despite their limited number.

  • They had back up containers of torpedoes for when they did run out, they had to retreat from the action and surface to access them.

  • Using deck guns is quite a slow process, not only do you have to man the gun (total of six men, on later subs it was 13), you have to remove the waterproofing devices (bungs, tompions, etc), you also have to bring up and install the gun optical sighting equipment which is not stored on the gun. Then you have to get all that down again before submerging. This is true for German type VII submarines (as U-96 was) though - other navies and models would have different practices and experiences.

  • With deck guns, it might take up to four shots to find the right range to target.

  • Where the deck gun has been used with success, it was nearly always on smaller targets, such trawlers and similarly sized vessels. So size (and range) played a important role in whether using a torpedo or the deck gun.

  • There are a number of situations where the target did not sink, and after they did eventually sink it (many hours later), it transpires that some loss of (passengers and) crew was as a result of that following up action.

By the time the author was on board, those events had passed and would have been in the log book and the crew accessible to talk about it; it was its seventh patrol and that included the event portrayed later in the movie, with them heading for the Strait of Gibraltar, being attacked, taking damage and limping for an alternative port.

(In reality U-96 survived as a training vessel for the last 2 years of war and was already decommissioned by the time it was sunk)

For torpedo backups:

TYPE VII U-BOATS, Robert C. Stern

fourteen torpedoes - four loaded in the bow tubes, four stowed at the bottom of the forward torpedo room (and two stored above floor plates), one loaded in the stern tube, one internally below the stern tube, two stowed externally under the deck outside the pressure hull.

So U-96, after running out of loaded torpedoes, they had to surface to extract the ones stored externally, before they could fire the finishing shots.

To get ammo to the deck gun, it was also quite a long winded affair with no electric loader or hoist:

The shells were stored under the floor planks near captains cabin. The shells were in individual metal containers. The shells were lifted by hand to the conning tower. From there they were lowered to the deck using a slope, for the gunners to pick them up.

U-Boat War Patrol - The Hidden Photographic Diary of U-564

It would appear that the reason for the torpedo rather than gun is that:

  • a quick send off to a stubborn target
  • it would take, altogether too long to get a gun crew up and running to finish off a target whose size might be too big to sink quickly
  • the target size for the gun is too big, they usually save it for trawler-sized targets
  • one torpedo is enough, its a balance of using what you have and coming back with confirmed kills than coming back with too many torpedoes because you kept 'saving' them







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