I’ve seen pictures and movies of WWII era submarines, and most of them have a cannon on top. How did they keep it from rusting? And how did they keep it lubricated and water tight so that it could be fired?
They kept it from rusting the same way the US Military has always kept stuff from rusting: constant mantainence.
The bore was plugged and the breech sealed (sometimes just with grease) and the whole thing covered with caps, covers and tarps. Everything was heavily greased and regularly so. Even then, it was a chore to get the thing unwrapped, drained, checked, loaded and ready to fire.
They were, by the way, of course never fired underwater. They were for use only while surfaced, as an anti-aircraft defense, to a limited extent shore bombardment, and in addition to torpedoes for attacking other ships (or ‘finishing off’ crippled ships without wasting another torp.)
Yeah, it would have to be heavily preserved to keep all the sea water from rusting it.
So I guess those movies which portray the sub surfacing and the crewmen climbing out and immediatly firing the cannon are a load of BS!
Actually, its not bs. I remember at least one account about the crew of a German U-boat doing exactly that. Unfortunately, real life cannons tend to blow up when you try that.
True, BUT, not significantly different than the forward guns on a destroyer. Salt spray is pretty nearly as corrosive as immersion and all naval weapons must be maintained regularly.
Not really. I’ve seen a Nazi type VII sub up close, the gun simply had a stopper in the gun barrel - and in the B&W contemporary movies they showed, no other special preparations were made. The breech, after all, is a gas-tight seal. It’s a matter of unscrewing the stopper, opening the ammo hatch, loading and firing.
That being said, there was rarely a need for great speed - if the situation posed a danger for the gun crew, the sub would stay submerged and either stay back or use torpedos to fight instead.
The deck gun was mainly an effort to increase the sub’s usability as a commerce raider - artillery shells are cheaper and easier to store than torpedos, and cargo ships don’t fight back very well.
I just wanted to emphasize to the OP that the proper naval terminology for the weapon in question is a “gun”; it would never be referred to as a “cannon.” I mention this only because it hurts my ears. 
I would imagine the MG’s and AA guns on those submarines needed plugs/stoppers as well, right?
Try this link:
WW2 era subs spent 99%+ of their voyages surfaced like a regular naval ship, so maintenance was probably about identical to what a destroyer would use for a similar gun.
Also, it’s interesting to note, that until at least mid-war, the deck gun was considered the primary weapon of the submarine, the torpedos only being used in situations in which the deck gun couldn’t be used. It’s a LOT cheaper to destroy a ship with a few 105mm shells than a costly and bulky torpedo.
Can you explain this a bit more? In naval terminology, what’s the difference between a gun and a cannon?
(Sorry for the hijack…)
Also try this:
Were there subs that had 105 mm deck guns?
Did you try my link above ?
Might answer your question very quickly.
As to scr4’s Q
A gun has rifling and fires a shell, a cannon has no rifling and fires a cannon ball.
Having said that, old warships were armed with smooth bore cannon, firing cannon balls, but were always designated according to how many guns they had.
38 gun Frigate, 98 gun ship-of-the-line etc etc
Some U-boats in the German service did mount 105-mm guns. The most common U-boat variant, the Type VII, had an 8.8 cm gun, but the ones with larger decks, like the Type IX, sometimes mounted 105-mm weapons. On April 19, 1942, U-130 actually used its 105-mm gun to bombard oil storage facilities on the island of Curacao, deep in the Caribbean.
The Type XI U-boat was planned to mount FOUR enormous 127-mm guns (they were actually called “U-Cruisers”) but the project never even made it as far as the beginning of the war, I would assume because it was a really stupid idea.
Deck guns were removed from U-boats in 1943/1944 when greater Allied efforts against submarines made them more trouble than they were worth.
American WWII submarines sometimes mounted weapons as large as 5 inches (about 127mm.) In contrast to the German experience, American subs mounted more and more deck armament as the war went on, and by war’s end it wasn’t uncommon for American subs to carry TWO 5-inch guns, plus an assortment of anti-aircraft weapons of varying size. This is because, in contrast to the Allies in the North Atlantic, the Japanese never really put together an effective submarine defense program.
The British M-Class of the 1920’s had a 12 inch gun.
It was not a very successful.
It seems as if there were two types of submarine deck guns, “wet mount” guns and “dry mount” guns. The closest thing I can find to an explanation comes from here:
So, am I to understand that many of these weapons did not require a tompkin (plug) for the barrel?
And the Germans lost nearly 800 U-Boats.
Some deck gun crews were killed when they forgot to take out the plug in their haste to attack a target, and the gun exploded.