prototypes were built from existing aircraft and flew in 1978. The US government was content to continue if a major foreign buyer was found and Britain had a plan to improve the Harrier with a new, larger metal wing. In 1980, the UK considered if the American program would meet their requirements – their opinion was that it required modification, thus the MDD wing design was altered to incorporate the British-designed leading-edge root extensions. In 1982, the UK opted to become fully involved in the joint US–UK programme. The US and UK agreement to proceed included a British contribution of US$280 million to cover development costs to meet their own requirements and to purchase at least 60 aircraft. The UK agreement included the involvement of British Aerospace (BAe) as a major subcontractor, manufacturing sections such as the rear fuselage for all customers of the AV-8B. The Harrier II was an Anglicised version of the AV-8B, British Aerospace producing the aircraft as the prime contractor, with McDonnell Douglas serving as a sub-contractor; final assembly work was performed at Dunsfold, England. The first prototype flew in 1981, first BAe-built development GR5 flew for the first time on 30 April 1985 and the aircraft entered service in July 1987. The GR5 had many differences from the USMC AV-8B Harriers, such as avionics fit, armaments and equipment; the wing of the GR5 featured a stainless steel leading edge, giving it different flex characteristics from the AV-8B. In December 1989, the first RAF squadron to be equipped with the Harrier II was declared operational. Description and role The Harrier II is an extensively modified version of the first generation Harrier GR1/GR3 series. The original aluminium alloy fuselage was replaced by one made extensively of composites, providing significant weight reduction and increased payload or range. A new one-piece wing provides around 14 per cent more area and increased thickness. The wing and leading-edge root extensions allows for a 6,700-pound (3,035 kg) payload increase over a 1,000 ft (300 m) takeoff compared with the first generation Harriers. The RAF's Harrier IIs feature an additional missile pylon in front of each wing landing gear, as well as strengthened leading edges on the wings in order to meet higher bird strike requirements. Among the major differences with the American cousin, was the new ZEUS ECM system, also proposed for the USMC AV-8 (which retained, after an evaluation, the original