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In the movie U-571 (IMDB) there's a scene where two U-boats fire torpedoes at each other, at close range, while both submerged.
I always imagined U-boats would fight one another while on the surface, with their deck guns. Use of torpedoes underwater adds the problem of the third dimension, thus hitting an underwater target would be very improbable and a waste of ammunition.
I am sure modern submarines have no problem firing at each other in 3D space, but I'm not convinced that the scenario I describe has never happened with their WW2 predecessors, however unlikely.
Are there any references to this tactic?