Well my problem was this:
Once you fire a torpedo, every single sub in the neighbourhood goes active. So much for secrecy ey.
To me, that's just not much fun. Doesn't matter if the power is low - even at Active at -50 you still see the yellow bearing line, and so it will reveal the enemy's location.
But you are right, FPSchazly... sometimes you can't find the enemy anymore. That's either a lost mission or you go active yourself to wake them up... Sometimes they fire a bearing-only torpedo and it gives you a hint of where they are.