Despite being a development of the Mark 8 SDV, the Mark 9 is a very different vehicle, designed for attacking surface ships rather than deploying SEAL teams on clandestine operations. Indeed, the Mark 9 and Mark 8 share very few common parts. The Mark 9 carries two SEALs, a pilot and a navigator, and two Mark 31 or Mark 37 torpedoes for standoff attacks against ships. These torpedoes can travel up to in a straight line, carry a warhead, and are capable of sinking ships as large as cruisers. In addition to torpedoes, the Mark 9 also carried limpet mines and satchel charges in a large cargo compartment aft of the pilot and co-pilot.