[Sailor Steve]

And now for something completely different: the reality.

1) Corvettes were indeed sunk by torpedoes, some of them almost certainly with impact pistols. This is also possible in the game, it just doesn't happen all the time.

2) In stormy weather it was difficult to attack anything. Whole convoys would sometimes turn into the wind and become stationary, using just enough power to mantain direction and position. The u-boats couldn't do anything about it, because torpedoes were just as useless in extremely heavy weather as deck guns.

3) Shooting corvettes with deck guns: In real life the corvette has pretty much the same gun as the u-boat, with one major difference: it takes quite a few 4" shells to put down even a 900-ton surface vessel, while a submarine is just waiting to sink. Even it one hit doesn't sink the u-boat, it will almost certainly turn it into a very poor surface ship.

"But if I surface behind him, he can't bring his gun to bear!" Nicholas Monsaratt recounted one time a u-boat tried this; the 40mm AA gun at the stern of the corvette promptly killed every German sailor who tried to get to their deck gun. The u-boat never had a chance.