The way I was taught this is that the strongest force and impulse (integral of a force over the time interval) is upwards after the explosion. The ship is already structurally destroyed at this point. Nothing works even if the ship does not immediately sink. When the ship falls donwards is when the keel breaks, hull breaks and water gets in. Any subsequent oscillation can cause more damage.
I know this is actually very important and interesting in the context of understanding how to build better ships/torpedoes, but I'm just imagining two seamen clinging to debris arguing on the exact mechanics by which the torpedo blew up their ship.
