The US forces have been operating their own version of the Harrier for some years. Known as the AV8 it performs an important role in the US Marine Corp. The first of these aircraft in US service were Harrier AV8A machines, these were delivered in 1971. Furthur development has been made by both Hawker Siddeley (British Aerospace) and McDonnel Douglas. Uprated AV8B aircraft with increased power and load capability entering service. The VSTOL ability of the harrier has always given a significant tactical advantage to the force that operates the aircraft. The ability to fly off roads, forest clearings, small carriers and ships without the need for a long hard surfaced (easily knocked out) runway offers huge benefits. It also allows the aircraft to operate close behind the lines.