Hi Tom,

Here is what little I have pieced together about this topic. I am also quite interested in it and I hope others will fill in the blanks and correct my misconceptions.

Main guns – (88mm & 105mm).

Both had a plug for the barrel that had to be removed before the gun could be safely fired and was supposed to be replaced before diving. The optics were removable and were not kept mounted all of the time. I think (but am not sure) that they were kept below and mounted on the gun when they were going to fire it and removed and taken back below before they dived. Ammunition was stored below and passed up through the conning tower hatch and unused ammo was passed back down before diving. Of course in a crash dive I suspect they just threw it over the side. The type IV had a “ready locker” in the deck by the gun. It contained a few rounds so the gun could be brought into action in a hurry. I believe the ammo in the ready locker was kept in individual, pressure-proof containers, but I am not sure. I have seen one of these containers, I am just not sure if they were pressure-proof or if the locker itself was. I don’t think the type VII had a ready locker but I am not sure. The main ammo locker in a type VII was in the floor between the radio room and the Captain’s quarters right outside of the control room. I am not sure where it was on a type IV but I think it was in the same place or perhaps under the control room. This ammo was kept in individual containers which I think may have been cardboard. The crew periodically removed each round and cleaned and greased it. Sometimes they had some tracer/incendiary rounds as well as high explosive rounds. I also know of cases where 105mm rounds penetrated almost all of the way through the side of a ship before detonating on the other side. I don’t know if it was a faulty fuse or if the fuse could be set for a delay. I also read somewhere that someone fired a 105mm gun at an attacking airplane (actually, I think they shot it down), but I can’t remember where I read it. Perhaps they had a few AA rounds for these guns as well.

37mm deck gun – on the early type IV’s. I know little about these other than they were single shot like the bigger deck guns. I suspect they were treated like the bigger deck guns but would really like to know for sure. I also think that the optics were removable and stored below like those for the bigger deck guns but again I am not sure. I think that this gun was meant to be used as an AA gun but I know of cases where it was fired at ships (along with the deck gun), so they may have carried more than one type of ammo for them including tracer/incendiary rounds.

Larger AA guns – The early single barrel 2 cm gun was kept in a pressure-proof container outside the pressure hull. It broke down for storage. It had to be assembled to use and broken down for storage before diving. I don’t know where its ammo was kept. Later on they did whatever they had to do to allow it to be mounted all of the time. As far as I know, all of the 2 cm & up AA guns after this time were just left in place when diving. I don’t know if any of these had optical sights.

As time went on, and the configuration of the wintergarden changed, they had ready lockers for their ammo as well. I suspect the rest of the ammo for these guns was stored in the main ammo locker with the deck gun ammo. I do have a photo of a stack of AA ammo (in clips) in the control room of a sunken U-boat but I don’t know if it was normally kept there or if it was being cleaned when the sub was sunk. Perhaps it was being staged to pass up to the guns. These guns were also used to fire at ships, so they probably carried a variety of types of ammo for them including tracer/incendiary rounds.

Smaller AA guns – The very small ones (MG 34’s, etc.) were always stored below, brought up for use and returned below before diving as far as I can tell. I don’t know about ready lockers for their ammo. These guns were also used to suppress fire from armed merchant ships.

Some U-boats later in the war had 2 - twin Breda heavy machine guns (Italian - 13,2mm) kept in pressure-proof containers on the conning tower extensions. As Rainer says “one opens the lids and guns ready to fire pop up”. I don’t know if the ammo for them was kept in a ready locker but you would think it would be because the guns were.

Some U-boats carried 2 - twin MG 81z’s (as I just found out from another post on the forum). These guns had a very high rate of fire (7.9mm / over 3,000 rounds per minute). I don’t know about ammo storage or types for them. I also don’t know if they were dismounted and taken below before diving of if perhaps they were kept in pop-up containers like the Breda’s.

Small arms – different boats carried different small arms but you might expect to find some combination of standard issue rifles, handguns (Walther P-38’s and / or Lugers) and machine pistols. Hand grenades were also carried some times. On at least one U-boat I know the guns were kept in a locked chest in the Captain’s quarters. I am not sure where the hand grenades were stored, perhaps in the main ammo locker. Some individuals also kept personal handguns although it was not authorized.

I am sure all of these weapons had to be cleaned and greased pretty often and their ammo would have had to be kept clean too but I don\'t know how often.

All in all, it must have been a mad scramble to bring the guns into action and to get everything back down that small conning tower hatch during a crash dive. I would be very interested to know what (if anything) was actually taken below during a crash dive.

I would be grateful for any additions or corrections to the above.

Regards,

Ken Dunn