Hi Tom,

Here are the best numbers I can come up with at the moment. They aren’t very good but I will keep looking and perhaps I (or another forum visitor) can improve on them.

1. Length and diameter of torpedo tube. From Miller: Torpedo was 21 inches (533mm) in diameter and 23.5 ft (7.16m) long. This probably did not include the length of the detonator fitted to the warhead which would have added perhaps 12 inches or so to the length. There also had to be room for the plate and that was perhaps 3 more inches. I haven’t been able to find the actual diameter and length of the torpedo tube even in Gröner or Rössler so at this point I am afraid we will have to assume the length and diameter of the torpedo tube from the measurements of the torpedo. It fit pretty snugly so the diameter would be close to the diameter of the torpedo. As to length I can only guess it was around 25 feet.

2. Pressure of air used to eject torpedo. From Gannon: about 24 atmospheres. From Miller: the torpedo was propelled at approximately 33ft/sec (10m/sec). Plate weighted 77 pounds (35kg). From Campbell: total weight of G7e: 3534lbs (1603kg).

3. I was also able to confirm Robert’s diameter of the conning tower hatch. From Köhl and Niestlé: 600mm.

4. I would guess a U-boat commander would weigh around 150 pounds or so and perhaps less. They weren’t generally very large men.

Sorry I don’t have better numbers. I know they exist somewhere and I may even have some of them in my U-boat books but it may take some time to find them. Perhaps another forum visitor can help us.

I think your sequence of events during the firing of a torpedo is correct.

The internal volume of the U-boat is probably a critical variable and I have no idea how to come up with it. When fully provisioned there was barely room inside to walk around and there was food and other things hanging from the ceiling too but there was much more room half way through the patrol after much of the food had been consumed and some of the torpedoes fired etc. Somewhere I have seen a breakdown of the food carried for one patrol and perhaps I could come up with its total weight but not the amount of space it took up. Again perhaps someone can help us with that.

Thanks much for attempting this. Your calculations can’t be any better than our estimates of the variables involved and we already know they aren’t very accurate but even a ball park result should be of some help in determining how common the overpressure was.

Sources:

Campbell, John. Naval Weapons of World War Two. Annapolis, MD: Naval Institute Press, 2002. ISBN: 0-87021-459-4.

Gannon, Michael. Black May. New York: Dell Publishing, 1998. ISBN: 0-440-23564-2. Copyright: Michael Gannon, 1998.

Gröner, Erich. German Warships 1815-1945 Volume Two U-boats and Mine Warfare Vessels. Annapolis, MD: Naval Institute Press, 1991. ISBN: 1-55750-301-X. Copyright: Bernard & Graefe Verlag, 1983 and 1985.

Köhl, Fritz and Niestlé, Axel. Vom Original zum Modell: Uboottyp IX C. Koblenz: Bernard & Graefe Verlag, 1990. ISBN: 3-7637-6005-9. Copyright: Bernard & Graefe Verlag, 1990.

Miller, David. U-Boats The Illustrated History of The Raiders of The Deep. Dulles, VA: Brassey’s, 2000. ISBN: 1-57488-246-5. Copyright: Brassey’s, 2000.

Rössler, Eberhard. The U-Boat - The evolution and technical history of German submarines. London: Arms & Armour Press, 1981. ISBN: 0-85368-115-5. Copyright: Lionel Leventhal Ltd, 1981.

Regards,

Ken Dunn