Hi Richard,

First, I am not a gunner’s mate. That said, the real answer to your question is that they didn’t keep them from rusting up. However different guns had different problems.

The deck guns

The 88mm and 105mm deck guns were actually very reliable. I have never heard of one of them failing to fire for any reason other than bad ammo (however that isn’t to say it never happened). These were artillery pieces with very few moving parts required to fire them. In one well documented case one fired with its barrel plug still installed blew the front part of its barrel off. They sawed off the bad part of the barrel and the gun was able to fire again.

However these guns had elaborate and complex mechanisms that had to be used to train and aim the gun and deal with the recoil and they had to work or the gun was useless. To keep them working they had external grease fittings all over them. These could be serviced at sea with a grease gun without disassembling them. You won’t see the grease fittings on most photos of these guns because they are hard to recognize but the 88mm U-boat deck gun at the U-boot Archiv in Cuxhaven has the fittings painted red so they stand out and I counted 50 of them before I stopped counting the last time I was there.

These guns had both barrel plugs and breach plugs which needed to be removed before firing and replaced before diving. Their optics were kept inside the boat and brought up & installed for firing and removed and taken below before diving. Of course this didn’t always happen when crash diving. Photos showing the barrel plug are numerous but photos showing the breach plug in place are rare but they are out there.

Ammo for these guns was kept clean by the crew. Each round was stored in its own watertight canister. Some of these canisters were kept in a ready locker in the deck close to the gun. The rest were kept in the magazine inside the boat. The crew routinely (every couple of days) removed some of this ammo and cleaned it before putting it back in the canisters.

Incidentally, the barrels of these guns were cleaned like you clean your single shot rifle at home – with a big cleaning rod and a wad of cotton and some solvent. I don’t know if they had a bore brush but I suspect they did.

There was also a 37mm deck gun/AA gun that worked just like the 88mm/105mm guns. You opened the breach, manually inserted one round, closed the breach, fired, opened the breach to expel the spent cartridge and manually inserted the next round etc. One like this was used on the milk cows as a deck gun and there was one like this used as an AA gun by early Type IX boats. On the Type IX boats it was mounted on the deck aft of the conning tower & wintergarden. It was a poor AA gun but was used during attacks on merchant ships as another deck gun. These were removed as the war progressed along with the deck guns and are not the 37mm AA guns we normally think of when we are talking about U-boats – those were full auto.

I have never seen one close up but I assume it had grease fittings for its mount and perhaps on the training gear too but I don’t know for sure. At any rate it also had a barrel plug and a breach plug though photos showing either one are rare. I have never heard of one of these guns failing to fire for other than bad ammo.

AA Guns

These were fully automatic and clip fed 20mm or 37mm guns.

The most well known is the 20mm gun. It came in a single mounting (1 gun), a double mounting (2 guns) and a quad mounting (4 guns). At the beginning of the war U-boats only carried the single mount.

In fact the small prewar Type II boats sometimes used one of these as their only deck gun/AA gun. They were kept (dissembled) in a canister that looks like a 55-gallon oil drum (though slightly smaller) and the canister was located on the deck in front of the conning tower where a normal deck gun would go on a larger boat. They had to open the canister, remove the pieces, assemble the gun (starting with installing the barrel) load & fire it then put it all back in the drum before diving. There was also one or two full magazines in the canister. It shouldn’t have had many problems as it was dry in its canister and most of these boats were used for training and were back in port every night where the guns could be maintained as necessary.

This was a peacetime idea that very quickly fell by the wayside once the reality of war set in and the canisters were done away with and the gun left mounted at all times. The larger Type VII & IX boats had then mounted on their wintergarden (without the drum of course) for the rest of the war. Of course that’s when the real problems started.

When they could be properly maintained these were reliable & accurate 20mm AA guns. This was somewhat possible early in the war but not as the war went on. They did carry some spare parts including barrels however with only one AA gun it was dangerous to take it apart during a war patrol for cleaning/maintenance as they needed to have it ready to fire as soon as they surfaced. It was big and heavy so it was not easy to move around and I think if they had to work on it they removed the appropriate parts and took them below to work on while they were submerged. These guns had in excess of 15 grease fittings that could be serviced without disassembling anything.

At any rate these guns jammed and otherwise malfunctioned quite a bit during war patrols. U-boat KTBs are full of references to problems with these guns. However any machinegun will malfunction if you fire it enough and not all malfunctions are due to the gun. Ammo problems frequently cause jams, failure to feed, failure to extract and even worse, the explosive rounds can go off while still in the barrel. Barrel obstructions can cause a blown barrel as well. These guns did have barrel plugs (they didn’t have a breach plug because the bolt was closed when they dived) however photos showing the barrel plug in place are very rare for these guns giving the impression that they weren’t used often.

About all they could do is test fire these guns as soon as they surfaced and try to deal with any malfunction on the spot. There were a number of cases where the test firing worked but they failed as soon as they tried to fire a complete magazine.

Well having U-boats out there with just one unreliable AA gun finally got someone’s attention and they went to the double mount then with two double mounts and they finally added the quad mount. That way if one gun failed they still had the other(s). Needless to say they also had failures in multiple guns during the same attack too.

The 37mm AA guns had the same problems and failed frequently though I don’t know how many failures were the fault of the gun and which were caused by the ammo. There was a single mount and a double mount. The double never worked very well and were prone to jamming. I don’t know about barrel plugs for these guns but they did at least carry spare barrels and probably other spare parts as well.

The gunners just did the best they could and tried to care for their guns whenever they could but there were still a lot of malfunctions.

I suspect the mounts for the 37mm guns had grease fittings too but I have never seen one close up to tell for sure. At any rate I have never heard of any of these rusting in place such that they couldn’t be traversed or aimed but again that doesn’t mean it never happened.

Other firearms

U-boats carried at least one MG 34 machinegun (later in the war they carried several) as well as rifles & pistols, and machine pistols. All of these were kept inside the boat until needed and returned to the inside of the boat when they weren’t. That doesn’t mean they had no environmental problems though. The inside of a U-boat was a damp nasty place.

After the patrol

The MG34s and small arms were all turned in to the armory after each patrol and reissued before the boat left for its next patrol. Someone in the armory cleaned and serviced and rebuilt them if necessary before they were reissued. The bigger guns were worked on, rebuilt, or replaced while in port too of course.


Well that’s about all I can add to the confusion for now. Some boats had no trouble with their AA guns and others had nothing but trouble with theirs. Again though it is impossible to know how many malfunctions were due to ammo problems and how many were due to a failure of the gun.

It would appear that the grease fittings on the mounts & some other moving parts of these guns did their job very well as I have never heard of any of these guns from the deck guns to the AA guns ever freezing/rusting such that they couldn’t be traversed or elevated. All the problems had to do with failures to fire, jams, or the gun (barrel) blowing up.

It is amazing that these guns worked as well as they did considering the conditions they had to operate in though. They were all (but the MG 34s & the small arms) painted with a rust inhibiting paint on the outside but there wasn’t much that could be done for the moving parts inside them. I don’t know what type of metal they were made out of but over the course of the war you would think they would try to make them (at least the ones used on U-boats) more reliable (drain holes for accumulated water, critical parts made out of rust resistant material etc.) but I have never found any documentation on this. If you do, please let me know.

Hope this helps.

Good luck finding a U-boat gunner to answer your questions. I would love to talk to one too. (-:

Regards,

Ken Dunn