Das Boot Surfacing Scene

[dfrighini]

Destroyers, in general, were terrible passive sonar platforms. They had a lot of self noise and at that time weren't designed with noise reduction in mind. I'd think it would be very hard to detect a submarine that way unless it passed very close to the destroyer, especially if the submarine was trying especially hard to be quiet. I don't recall ever reading of a WWII destroyer making initial detection on a submarine passively.

This is very true, also destroyers could not really use there active sonar over 12 kts. I presume if they were trying to listen with passive sonar they would stop dead in the water, but this would leave them vulnerable to attack from the submarine.

[tommy303]

The submarines I was on never used compressed air to reduce ballast except in an emergency. For one thing, it's much noisier than a pump by I'd guess several orders of magnitude. Our trim pumps were designed to operate at our maximum depth.

I am not sure about the depth limits of the trim pumps on a U-boat, aside from the fact that they could be used down to the boat's safe diving limit. The boats could generally dive much deeper in emergencies, but at depths around over 200m the pumps had a much harder time. It is true that on German U-boats, use of compressed air was only an emergency proceedure, even in normal surfacing (as it would take time to recharge the compressed air resevoirs from the compressor). The usual proceedure was to use the pumps to bring the boat to slight positive buoyancy and use hydroplanes and motors to drag it to the surface. Thereafter, the external tanks were blown by admitting diesel exhaust into the tanks while the main internal dive tank was pumped out to the required level. Actual use of compressed air was pretty much for emergency surfacing.

Destroyers, in general, were terrible passive sonar platforms. They had a lot of self noise and at that time weren't designed with noise reduction in mind. I'd think it would be very hard to detect a submarine that way unless it passed very close to the destroyer, especially if the submarine was trying especially hard to be quiet. I don't recall ever reading of a WWII destroyer making initial detection on a submarine passively.

This is generally an accurate statement, as destroyers often operated most of the time at or beyond the limits of hydrophone effectiveness. They were not designed around strict ASW roles since they were primarily escorts and offensive weapons for the fleet. ASW was secondary to their other combat roles. A good many smaller vessels, such as sloops and frigates (or DEs) operated at lower speeds and were better at the ASW role; it should also be remembered that in 1940-early 1942 many proper ASW ships were not yet equipped with active sonar or ASDIC as supply was not up to demand, at least in the Royal Navy. in addition, quite a few small trawlers and drifters were given hydrophones in coastal waters such as the straits where they performed picket duties. Generally limited in their capacity to engage a submerged U-boat, they could still provide a line of mobile listening posts and call in the ASW sloops or DE's should something be picked up.

[marcelo_malara]

Hi guys. I watched the film tonight, third time but the very first since I became a naval history enthusiast. The level of detail is just amazing, it must rank as the most accurate naval film ever, along with Master and Commander (and of course Pearl Harbour...just kidding). A couple of questions.

-Is all the equipment correctly reproduced (aside from the Enigma mentioned above)?
-Was a full scale mockup used for some scenes? I can tell that it is lacking the weldings in the hull, so it must have been made of plastic (?).
-Where were the port scenes shooted?
-May be there is an error in the scene of the captain trying to torpedo the destroyer? I mean he didn´t seem to track the ship long enough so the computer can solve the shooting problem.

[Karl Heidenreich]

A friend of mine told me that he went into the sub mock up somewhere in Bavaria or such. But that was many years ago.

[RF]

-May be there is an error in the scene of the captain trying to torpedo the destroyer? I mean he didn´t seem to track the ship long enough so the computer can solve the shooting problem.

I thought it was the ''bow on'' shot, for which you wouldn't have time for a computer solution.

From what I recall the commander didn't have the time to commence the attack before the destroyer was upon him and the sub had to crash dive.

Another point - if torpedoes had been fired at such close range and hit the target so it blew apart wouldn't there be a danger of the sub being struck by the debris?

[tommy303]

Another point - if torpedoes had been fired at such close range and hit the target so it blew apart wouldn't there be a danger of the sub being struck by the debris?

I don't know about debris, but if the torpedoes weren't fired at at least 1000m, the oncoming destroyer and the torpedoes would have met before the torpedoes could arm themselves. The G7a and G7e required runs of about 450m to arm and become active.

[RF]

The view shown in the periscope would have the destroyer at less than 1000 metres, insufficient time to launch the torpedoes let alone arm them.

[Bgile]

The view shown in the periscope would have the destroyer at less than 1000 metres, insufficient time to launch the torpedoes let alone arm them.

How do you know what power he was using?

[marcelo_malara]

Is there any case of a warship torpedoed dead on?

[tommy303]

There were a few instances, but a lot would depend on the torpedoes being used. The G7a and e used an exploder or pistol unit which in theory should have worked great for such shots, but in reality did not. The pistols in question, Pi I and II had a set of four levers which acted to transmit the shock of impact to the firing pin (as well as magnetic function which was found to be faulty in conception). The idea of the levers was to insure proper detonation at up to 70* obliquity, but it was found out by Admiral Kummetz, that testing of the device had been confined to just two shots with mixed results. It was found that too great an obliquity or if striking a very curved surface and the blow, instead of falling on the levers, would instead be taken on the ogive of the torpedo head--thus no detonation. Subsequent testing showed that the practical limit was closer to 30* obliquity. Thus in a head on torpedo shot, neither the Pi I or Pi II could be expected to work properly as the angle would be too oblique.

The situation was eventually solved in 1942 after developing a simpler and more reliable pistol based on British ones recovered from HMS Seal. The irony of this is, the Germans were thus using a copy of a British pistol which in turn was a copy of the very reliable German WW1 torpedo pistol.

[marcelo_malara]

Thanks Tommy. So the skipper wouldn´t have tried such a shot.

[Bgile]

There were US submarines using that tactic after the torpedo problems had been corrected. The best thing the destroyer can do is keep coming and hope they miss. If he turns, he swings his stern out and presents a bigger target.

[marcelo_malara]

I think that the bow wave of a ship coming at 30 kt would have an effect on the trajectorie.

[tommy303]

So the skipper wouldn´t have tried such a shot.

I suppose if he felt lucky he might try it. There is always a chance it could work, but personally i would want to use those few minutes of grace to get as much water between me and him before the depth charges started coming down.

[marcelo_malara]

And there is also the question of the accuracy. A destroyer is, what? 10 meters wide? That would be 10 mils at 1.100 yards. Is the torpedo capable of mantaining course with that precision?