[Shadriss]

You missed the first part of that reply, or rather you didn't get the implication. As the ship is sinking, it's putting off a LOT of noise that it normally wouldn't, all of it in the Broadband range. In addition to the much reduced air volumes that would hamper the active return, that same active return also now has to contend with a much higher local ambient noise. In essence, the echos would be lost in the background noise of that event, so the torp still wouldn't get a return from it, just for different reasons.