What you have is the fantasy of just about every sub skipper of the war: a submarine with no deck gun. The things were useless except for hanging laundry on. In practice they were more hazardous to the submarine and its crew than the enemy's guns. The very first man killed on an American sub during the war was manning the stupid thing when the enemy opened up and disassembled the poor guy who shouldn't have been there anyway. More effective than the deck gun was pointing your finger at the enemy and yelling "Bang! Bang!"
Deck guns subtracted underwater speed and contributed to louder submerged travel, making the submarine more detectable to enemy sonar. Cdr Dealey of the USS Harder, when asked whether he wanted his deck gun mounted fore or aft said "I don't care which, so long as it's on wheels so I can roll it overboard."
So let's check my FOTRSU S-boat and see if I have a deck gun. Never use the thing and I don't even know if I have one. Hmmmmmm.....
Crap! There it is, silhouetted against the control tower. Roll it overboard, boys!
