Bismarck construction flaws

Discussions about the history of the ship, technical details, etc.

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Javier L.
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Post by Javier L. » Mon May 23, 2005 1:54 pm

I agree that this "single layer" is a potential weak point but the exposed vulnerable bulkhead has a height of less than 1 meter. I'm afraid that a low-running torpedo (+8 meters) would always be very bad no matter if this flaw is present or not. Because of the curvature of the lower hull the overall depth of the TDS down there has only a couple of meters.

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Post by Tiornu » Mon May 23, 2005 3:16 pm

"This small design fault could be remedied quite easily with some protective casing, perhaps it was?"
If they didn't see fit to correct it between Gneisenau and Bismarck, they may not have given it any subsequent thought. As drawn in G&D, "H" has this feature as well.

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Post by phil gollin » Mon May 23, 2005 6:50 pm

Whilst I note that the bilge keel will protect the area to a small extent I cannot understand why the angled section of the side protection system isn't taken down to the joint of the double bottom.

Surely if the side protection is stressed by an expolsion the angle coming down on to the flat plate will flex, whereas if it came down at the double-bottom the joint would be stronger, or is that the intent, to leave some flexibility ??????????

Any torpedo hit would have to be very "lucky" (which Bismarck knows all about) as it would have to be below the bilge keel, but not too low as to hit the turn of the hull and not set of the fuse (depends on fusing of course).

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Torpedo depths

Post by Paul Harrison » Tue May 24, 2005 10:27 pm

This discusion is interesting in the context of the pre-war development of magnetic influence detonators for torpedoes, which the swordfish from Victorious launched at Bismarck. It is my undertsanding that these torpdeoes were intended to be set to run at a depth to pass just under the hull of the target ship, and detonate underneath the ship when they detected the magnetic influence of the ships hull. This would seem to place the intended point of expolsion very close to the vulnerable area. It is strange that this vulnerability was there as the german navy had developed a magnetic influence pistol for toprpedoes before the war.

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Re: Torpedo depths

Post by Patrick McWilliams » Wed May 25, 2005 9:37 am

Paul Harrison wrote:This discusion is interesting in the context of the pre-war development of magnetic influence detonators for torpedoes, which the swordfish from Victorious launched at Bismarck. It is my undertsanding that these torpdeoes were intended to be set to run at a depth to pass just under the hull of the target ship, and detonate underneath the ship when they detected the magnetic influence of the ships hull. This would seem to place the intended point of expolsion very close to the vulnerable area. It is strange that this vulnerability was there as the german navy had developed a magnetic influence pistol for toprpedoes before the war.
For a German perspective on the huge frustration encountered in torpedo performance, see the memoirs of Admiral Karl Doenitz (Ten Years and Twenty Years, Cassell, 2000). In short, they significantly overestimated their pre-war advances in magnetic (and indeed contact) torpedo technology and this led to significant golden opportunities being missed (e.g. Ark Royal, HMS Nelson). It also led to disciplinary action against the technical unit responsible for magnetic torpedo testing.

It's ironic that the nation whose submarines came within weeks of bringing Britain to her knees saw her brand new battleship disabled by the torpedo (contact variety).

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Post by tommy303 » Wed May 25, 2005 2:35 pm

An interesting aspect of the torpedo problem as experienced by the Germans in the first two years of the war is the failure not only of the magnetic detonators, but also the contact ones. In the latter case the firing trigger was incorporated in the blades of the arming impellor on the nose of the torpedo. When one of those was bent backwards on impact, it released the spring loaded firing pin; however if the angle was too oblique, or the torpedo hit a very rounded portion of the hull, such as the knuckle where the hull turned sharply towards the bottom. the impact would be on the ogive instead of the impellor blades (which were of smaller diameter than the nose), and this would lead to a dud. The eventual German solution was to copy an example of the British inertial firing mechanism which would fire the warhead when the torpedo decelerated on impact and which was less fussy about oblique hits. The irony was, if I recall correctly,the British mechanism was itself a copy of a German WW1 design.

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Magnetic torpdeo detonators

Post by Paul Harrison » Wed May 25, 2005 7:21 pm

I was aware of the problems with German torpedoes early in the war, I don't think that anyones early magnetic deatonators worked properly. Nonethe less having done the development and deployed the weapons you would have thought that ships anti-torpedo systems of the period should have been designed with an awareness of there expected mode of operation. Defensive systems are usually deisgned to combat the latest weapons technologies and anticipate future systems were possible. In Bismarcks case the aparent weakness as described seems to be in a very bad spot to resist the expected mode of operation (putting aside problems with the initial implementation of these systems) of the latest generation of torpeodes which were in use in the US / UK and German navies at the time of Bismarcks completion. I did wonder in the light of the Cameron foorage of Bismarcks rudder, whether the torpedo that struck Bismarcks rudder might not have had a Magnetic detonator, it would explain a detonation under the runnders, but thats just my idle speculation

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Post by José M. Rico » Wed May 25, 2005 8:29 pm

Just a quick note. All the torpedoes launched at the Bismarck by the Swordfish on 24 and 26 May, had contact detonators.

Magnetic detonators were used on the first air strike launched from the Ark Royal at 1450 hours on 26 May. This attack, however, turned out to be a failure since the Swordfish attacked the light cruiser Sheffield by mistake instead of Bismarck. Luckily for the British, the Sheffield was not hit by any of the 11 torpedoes launched because they had faulty magnetic pistols. Two torpedoes exploded upon hitting the water, three on crossing the cruiser wake, and the other six were successfully avoided. Therefore, the Swordfish returned to the Ark Royal and had their torpedoes armed with contact pistols this time for the final strike on the Bismarck.

Image
Photo. One 18 inch MK XII torpedo with its contact pistol fitted.
The moment the point of one of the "whiskers" strikes the enemy hull, the detonator is fired and the warhead explodes.

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Torpedo Pistols

Post by Paul Harrison » Thu May 26, 2005 7:01 pm

On what basis are you claiming that the torpedoes launched by Victorious had contact pistols. So far as I am aware the Duplex pistol used was capable of either contact or magnetic detonation. This was the pistol that had been used in the Mediteranean and in the attack at Taranto. I presume as this pistol had been in production and use for a while, and as Victorious was a brand new ship that the then standard practice would have been to use a Duplex pistol, as this was what Ark Royal chose to do in the same circumstances. I am sure that I have seen at least one account that indicates that a torpedo passed under sheffield without expolding, this would be the expected behaviour of a duplex equipped torpedo set to run at a depth to just pass under a battleships bottom, when passing under a shallower draught cruiser.

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Post by José M. Rico » Thu May 26, 2005 8:09 pm

Hello Paul,

The new duplex (magnetic) pistols were used against Sheffield, and later replaced by contact pistols for the final strike on the Bismarck. The torpedo that disabled Bismarck's rudders had a contact pistol.

As for Victorious Swordfish, I am not sure about it, but you might be right about the use of Duplex pistols. In any case the torpedo that hit Bismarck amidships on the starboard side on 24 May, is reported to have detonated after hitting the armour belt and not by the magnetic influence of the ship's hull.

José

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Duplex Pistols

Post by Paul Harrison » Fri May 27, 2005 12:04 am

I agree that the evidence is that Victorious hit the armour belt, I have seen it claimed in some accounts that the torpdeo malfunctioned and ran on the surface. I believe that as the duplex pistol seems to have been standard, and as Bismarck was the sole intended target in all three attacks, that the missions would have been planned as attacks with deep running torpedoes. When considering the aparent vulnerability in Bismarcks deisgn it is usefull to look at the likely weapons to be used against Bismarck. It seems to me that magnetic influence fused topedoes set to run deep were probably used against Bismarck by Victorious and were orginally intended for the attack by Ark Royal, so the prospect of a torpedo detonation in the vulnerable area were actually quite real.
I presonally have never seen any evidence that a different fuse was fitted in the second attack launched by Ark Royal, can you stipulate what type of fuse was used to replace the duplex fuse. I consider it rather odd that a backup contact only fuse would be carried in addition to a dual purpose fuse on a ship, why not simply set the dual purpose fuse into contact only mode assumung that this was possible. I suspect that this was a more likely secario. In this scenario it becomes plausible for a torpedo to be overlooked for fuse modification particularly if the crew is in a hurry trying to mount a second strike after a failed first one.

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Post by Javier L. » Fri May 27, 2005 3:31 pm

Thinking about this potential flaw. How well did the double bottom and TDS of the Tirpitz do when she was mined by midget submarines in Norway?
Any reports of this "single layer" failure?

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Post by Bgile » Sat May 28, 2005 5:27 pm

It's almost impossible to protect a ship against an explostion underneath it. Double or triple bottoms served as protection against grounding and small explosions, but a torpedo size explosion a few meters under a ship would do a lot of damage to the interior. One thing it wouldn't do is effect stablility as much as side flooding. Witness the German guided bomb which blew out the double bottom in one of Warspite's engine rooms.

Anyone know how much degausing equipment would affect magnetic influence torpedoes? Most WWII large naval vessels had it.

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Protection

Post by Bill Jurens » Sat May 28, 2005 10:32 pm

I find Tiornu's theory about the missing inner bottom interesting and well thought out, but I am inclined to doubt that the same blunder would apply through all of the ship classes mentioned, i.e. Bismarck, Scharnhorst, and the "H" class. It looks to me as thought it were more a geometric thing; the designer drew a line about 2.25 meters inside the shell plating -- which somebody probably told him was the desirable offset for a torpedo explosion space -- and that's where this line intersected the holding bulkhead. True, the inboard fuel tank does protrude outside this line quite a bit, but that may have been done for structural convenience, i.e. to enable one to maintain straight bulkheads in the fuel tank system. One can geometrically get a closer fit, but that would mean either having the second bulkheads heavily curved or 'broken' twice -- which would mean more weight and complication in joints, etc., or making the more vertical of the outboard fuel tank bulkheads too far inboard, thereby shrinking the tanks.

There are other problems as well. One must also keep in mind that this particular holding bulkhead flaw is far from the neutral axis of the ship, meaning that the plating would usually be under fairly heavy strain due to the ship working at sea, and that because it was fairly substantive structurally, it would also represent a 'hard/soft' discontinuity with the adjacent plating which would have been relatively thin. This sort of discontinunity, and the designer's inability to fair in the stresses to the adjacent structure is one of the main reasons why the stern came off.

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Post by Javier L. » Tue May 31, 2005 9:35 pm

Hi Bill,

I always thought the stern came off because it was hit by a torpedo. :D
I also fail to see the relationship between the "single layer" flaw and the collapse of the stern.

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