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. The Mark 9 is designed to clandestinely approach enemy vessels while submerged, surface to fire torpedoes, and then escape unnoticed. As such, its design incorporates stealth characteristics, including a lower profile and sonar absorbing materials. The Mark 9 SDV was intended to attack ships in shallow coastal waters that full-size submarines could not enter, and to draw attention of an enemy fleet away from the Mark 9's parent submarine. Though it proved very effective in exercises, the Mark 9 was retired starting in 1989 and was fully phased out of service by the mid-1990s due to manpower and budget constraints and because all of its capabilities save launching torpedoes were duplicated by the Mark 8. The pilot and navigator operate the vehicle from a prone position and lay side by side. The prone position gave the Mark 9 a low profile and enabled it to operate in very shallow water, although SEALs reported that staying prone for the entire duration of an operation was uncomfortable. The Mark 9's sleek profile and independent diving planes enabled it to be especially agile. It was also faster than the Mark 8, reaching speeds of , owing to its twin screw propellers and high-performance silver-zinc batteries. Its speed and agility led operators to compare it to flying a fighter jet or driving a sports car. Operational history The SDV is used primarily for inserting SEALs for covert operations or for placing mines on ships. It is also used for underwater mapping and terrain exploration, location and recovery of lost or downed objects, and reconnaissance missions. It has been invaluable at deploying SEAL teams in clandestine missions, as it has enabled them to land on shores inaccessible to a larger submarine with a degree of stealth greater than that offered by small surface craft, helicopters, or other means. In exercises, the SDV has been found to excel at anti-shipping attacks, being able to attack targets in heavily-guarded fleets or docked at military bases and then slip away undetected. Additionally, it can carry larger limpet mines than those carried by