I'd hesitate about letting the 12-sided die dictate your loadout. Are you really going to head out if you roll is a two or three? Unless you find a historical reference, who's to say your idea is realistic? From what I've read in many books, it wasn't a shortage of torpedoes that crippled the U-boat effort but a shortage of crews and boats and actual opportunites to get into firing position on a target, due to the highly effective ASW efforts of the Allies. Even fuel was getting pinched in the last year of the war, but they could get some by draining the tanks of laid up surface vessels.
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