Good question! I suppose a bug is a dud, right???
Also, in the graphics menu turn your 3d ship damage slider all the way up. You should see damage. If it is all the way up, and you didn't see any damage, then I suppose you hit the target, saw the splash, and the torp bounced off the hull. It happened that way alot during the war. What year are you playing. Daspit's attempt was on the 24th of July, 43. I believe the Navy got everything figured out by 44.