Hawker Siddeley Harrier AV-8As to the AV-8C configuration—the work focused mainly on extending useful service lives and improving VTOL performance. The AV-8C and the remaining AV-8A Harriers were retired by 1987. These were replaced by the Harrier II, designated as the AV-8B, which was introduced into service in 1985. The performance of the Harrier in USMC service led to calls for the United States Air Force to procure Harrier IIs in addition to the USMC's own plans, but these never resulted in Air Force orders. Since the late 1990s, the AV-8B has been slated to be replaced by the F-35B variant of the
Hawker Siddeley Harrier designated "P.1127 (RAF)", of which the first made its maiden flight on 31 August 1966. An order for 60 production aircraft, designated as Harrier GR.1, was received in early 1967. The aircraft was named after the Harrier, a small bird of prey. The Harrier GR.1 made its first flight on 28 December 1967. It officially entered service with the RAF on 18 April 1969 when the Harrier Conversion Unit at RAF Wittering received its first aircraft. The aircraft were built in two factories—one in Kingston upon Thames, southwest London, and the other at Dunsfold Aerodrome, Surrey—and underwent initial testing at