I have seen several ships that had sunk in deep water salvaged by cutting them into manageable sections. They use a heavy cable that has round carbide sections that slip on over the cable, maybe 6 -8" long and 3-4" in diameter. The cable is slipped under the ship and then pulled one way, pulled back, back and forth with tremendous tension on the cable . It cuts slowly but steadily until each section is freed from the ship, then lifted to the surface. Ok, the link below contains the cable rig, they did it a different cutting from top to bottom but the same idea, skip to 17 mins in and that is about where the cutting rig begins,