I have heard the question before, (asked it myself many years ago)...
Seems to me the answer was to keep rearming and continue hitting the sub. Did the trick with landing and rearming on the sub itself which was neat.
I never sunk the damn thing though. Kept getting target fixated and doing the kamakaze thing.
In a way I guess this has kept the game alive... damn, I think I'll try again!!!
I would love to get the source code and see how they made the flight dynamics seem so fluid on the old A500.