For another good Mk. 15 story, USS Nautilus fired a spread of torpedoes at the Japanese carrier Kaga during the Battle of Midway- the ship had already been hit by bombs and was burning furiously (and sank later anyway), but Nautilus' captain wisely decided not to risk the crippled ship being able to get her fires under control and limp home for repairs. (Note that this is exactly what nearly happened hours later a few hundred miles away with the Yorktown- if not for submarine torpedoes finally causing fatal damage the ship might have been towed back to Hawaii) Nautilus scored a single hit on the immobile Japanese flat-top...
...at which point the front half of the torpedo snapped off and sank to the bottom of the Pacific, while the second half bobbed up to the surface, where by some accounts some of the Kaga's crew used it as a life raft while awaiting rescue- in which case, Nautilus' torpedo not only failed to cause damage, it actually may have helped SAVE some of the crew.
