Shoot through every orofice you can, flaming sulphur bombs ... keep doing it for a full 24 hours or something.
Let a week go by, board the thing and sweep up the carcasses and feed the fish.
Just a thought
If they can find it a well placed torpedo would do the trick!
If this vessel poses such a threat, why not utilize maritime aircraft to locate it, and then sink it as a menace to navigation using either naval gunfire or a torpedo?