When U-Boats, and other subs, had deck guns, how well did they work after being immersed in saltwater?

Posted 15Nov2017.

I wrote this earlier under Stephen Carey’s answer, but since I had the time to elaborate a bit more, I am putting it under a separate answer…

Going off the top of my head as well, I would support your idea on the demise of deck guns with a couple more observations.

One of the prime motivating factors for mounting the various caliber guns on submarines was self-defense while the boats were on the surface. The nature of subs in the First World War was that of commerce raiding; to get to their patrol areas, they needed to move quickly and efficiently… which necessitated surface transit. The use of deck guns proved to be a matter of opportunity in a lot of cases, and it could be argued that they were — in some cases — more reliable than the prime offensive weapons. Now that I think of it, I would have to look up more on the practice of German U-boats facilitating the abandonment of merchant ships in this war… but that is getting off on another tangent.

The second point is the Guppy conversion after the Second World War. The installation of snorkels allowed for more submerged time, and the pressing need to increase submerged efficiency brought a campaign of streamlining the hulls — ditching anything which increased drag. Railings, anti-aircraft guns, and their associated platforms… all these went away when the conning towers/sails were reconfigured.

As for the preservation of the guns while submerged, again, I am going from memory. If I recall correctly, they were specifically designed “wet” mounts, modified to be sealed against seawater intrusion (sights), or coated to reduce the exposure to corrosive salt water (recoil and training/elevation mechamisms). As for the ammunition, it was stored either in waterproof trunks on the conning towers in relatively close proximity to the gun, or stowed in a magazine within the pressure hull. In the case of the American Gato, Balao, and Tench classes, these were usually below the galley/mess, and were the point of origin for an ammunition train once the boat surfaced and commenced engaging the targets with the deck gun.

Again, this is all from memory and I may be wrong on a couple finer points. I will double check later and revisit this post.

[Edit]

German employment of U-boats during the First World War was somewhat fickle at the beginning of the war:

Faced with the possibility that the U.S. might go to war over the incident, Germany backed down and ordered its U-boat fleet to spare passenger vessels. The order, however, was temporary.

However, the concept of “unrestricted submarine warfare” proved to be a necessity; during the Second World War, this lesson in the control of maritime sea lanes of communication was quickly remembered by the Kreigsmarine and further exploited by American boats operating against Japanese shipping in the Pacific.

A brief description of the different GUPPY modifications can be found here, but my initial ideas were close.

Concerning the deck gun design, I wasn’t too far off on the design features, according to one source:

The Mark 17 was a “wet mount” version for submarines and was unusual in that it did not require breech or muzzle plugs. This was because it used a special liner resistant to corrosion from sea water and could thus be submerged and flooded without harm to the gun.

As for the overall effectiveness of these deck guns, that information is buried within several books immediately behind me and in several sites bookmarked. However, this is Quora – not a Master’s thesis on comparative successes of submarine-facilitated naval gunnery. In general, they were quite successful in mitigating the frustration felt by American crews when forced to use the Mk 14’s at the beginning of the war (otherwise known as “the steaming hot mess from the Bureau of Ordnance”), as well as interdicting Allied shipping by German U-boats in the Atlantic. These engagements were driven by the immediate tactical and environmental considerations, but they were still very effective.