Gibsons
Lifer
I thought I read a while back about really fast torpedoes creating some sort of air bubble around them allowing them to go way faster. Would that change the "speed of sound" in water since the torpedo is encompassed in air? Regardless if it's faster than sound, if it's fast enough so that it's almost at your hull before you hear it then it's way to late to do anything about it.
Disclaimer: I don't know shit about torpedoes or Naval tactics and am not trying to claim that I do, so the above might be completely wrong.
That's the shkval, linked above. It's about 230 mph max per the link.