If the sub sank with loss of all hands--not unlikely if a torpedo went off in the tube--how did anyone know about this? A hell of a lot of submarines never came back to base in WW II, and in most cases a) there were no survivors, b) very little debris seen.

I also wonder about the basis of the story. The USS Tang was sunk by its own torpedo in October 1944. That leaves about 8 months for the changed torpedoes to operate.