[Mopp4]

...but that the explosive device itself did not come in contact with the hull of the South Korean ship, the official said.

Well, I'm no military genius but isn't that how a torpedo works...by coming in contact with the hull of a ship ????

[Rammer]

No, most torpedoes explode under the ship. The resulting pressure change breaks the ships hull.

[Strategerist]

Modern torpedoes generally have magnetic-influence detonators; they explode under the hull without making contact, creating a bubble of gas that breaks the keel - essentially the spine - of the ship so it splits in half.