The Patrol Air Cushion Vehicle (PACV), also known as the Air Cushion Vehicle (ACV) in Army and Coast Guard service, was a United States Navy and Army hovercraft used as a patrol boat in marshy and riverine areas during the Vietnam War between 1966 and 1970. Six hovercraft were built, three for the Army and three for the Navy. The military developed the PACV because its lack of draft meant that it could operate unimpeded in the shallow and reed-choked waters widespread in South Vietnam, most notably in the Mekong Delta and Plain of Reeds. The PACV was also found to be valuable because of its unusually high speed of , faster than other watercraft in the conflict. However, it faced major drawbacks, including its high cost of $1 million (equivalent to 13 Patrol Boat, Rivers) and unreliability. During the conflict, two of the Army's three hovercraft were destroyed by the Viet Cong. The PACVs in Vietnam were considered "unsuccessful" in evaluations and were withdrawn in 1970. Following their service in Vietnam, the Navy PACVs returned to the United States where they were used by the Coast Guard, where another sank in an accident. Development The PACV was based on the Bell Aerosystems SK-5 hovercraft; a licensed version of the British Saunders-Roe (later, British Hovercraft Corporation) SR.N5 hovercraft. The SK-5 was adapted for American military use in 1965. Three were purchased by the US Navy for operations in the emerging Vietnam War. Training of PACV crews was performed in the waters off Coronado, California near San Diego. Design of the Army ACVs began in 1966 and was completed Design Two different designs were made: one for the Navy and one for the Army. The Navy's hovercraft, called Patrol Air Cushion Vehicles, more closely resembled the civilian SK-5s that they were based on while the Army craft had more extensive modifications. Each hovercraft was long, with a beam of and a height of when floating on its air cushion. It weighed fully loaded. Army and Navy PACVs had a crew of 4—driver, radar operator, and gunners—and could carry up to 12 troops, many of whom rode on the outside of the vehicle. Both designs were powered by a General Electric 7LM100-PJ102 gas turbine engine. The engine, its 304-gallon (1,150 litre) fuel tank, an auxiliary power unit, and the Westland transmission were located amidships. The engine powered both the three-blade variable-pitch propeller