There are an astonishing number of movies and books that depict submarine warfare involving two submerged hunter-killers in a deadly game of cat and mouse that ends with one taking a torpedo amidships, sending the crew to Davy Jones’ locker. In reality, though, actual sub versus sub combat is extremely rare. Attack subs generally plied their trade against surface vessels, striking merchant shipping or taking out valuable flagships while trying to avoid destroyer escorts.
In the history of submarine warfare, there’s only been one known instance of a submarine taking out another submarine with a torpedo while both were submerged. In 1945, the HMS Venturer sunk the U-864 with a spread of torpedoes targeted like a shotgun blast in the hopes that one might strike their quarry, and they got lucky. The U-boat sank with all hands on board.
Now, a corollary to this is the fact that at the beginning of the Second World War, American torpedoes were utterly dogshit. So many of the early naval battles against Japan saw torpedo after torpedo failing to destroy or sometimes even hit their targets. The main issue was the steering mechanisms on the fish—they’d often come out of the torpedo tubes or launchers with their control vanes jammed, causing the torpedo to dive for the sea floor, or bob to the surface and lose speed, or sometimes even make a wide circle in the water and return to the vessel that fired it.
Which means that in the history of the silent service, more submarines have sunk themselves with torpedoes than have sunk enemy subs.