I've had the same problem with warships. During an attack on a convoy, I was targetting several ships. Lauched the topedoes, dived deep, and listened out for the explosions. One torpedo ran way over its time...then hit something.
Anyway, I tracked the convoy, did another attack, then carried on for home along the convoy's reciprocal. Suddenly I'm being fired at! OMG...its half a Flower-class coming at me! Only her forward 2/3 was visible and she was making a few knots, but even with her bow angled upwards she was still able to depress her main gun and aim at me
She had obviously got in the way of the torpedo that missed it's intended target, and ended up trailing the convoy.