Apart from the improved powerplants, the first four P.1127 prototypes were quite similar; the fifth prototype, "XP980", introduced the taller fin and tailplane anhedral which were later used on the production Harrier. The fourth machine was partially used to provide Hawker production test pilots with type familiarisation. The first carrier vertical landing was performed by the first prototype on in 1963. The last P.1127, "XP984", introduced the swept wing. It was eventually fitted with the 15,000 lbf (66.7 kN) Pegasus 5 and functioned as the prototype Kestrel. The first three P.1127s crashed, the second and third occurring during development. In 1963, the first prototype, "XP831", publicly crashed at the Paris Air Show; the accident had been caused by a speck of dirt in the air feed lines of the nozzle control motor, which had caused the engine nozzles to stick. "XP831" was later fully repaired and resumed development flying. All the pilots involved survived. By late 1961, Hawker had been able to demonstrate the validity of its design concept, despite a lack of support from the RAF and little from the Her Majesty's Civil Service. In early 1962, official support emerged in the form of the Operational Requirements branch of the Ministry of Aviation, which approached the Treasury seeking its sanction of a batch of nine production-standard aircraft to be operated by an evaluation unit to be administered by the Central Fighter Establishment at RAF West Raynham. In light of open interest expressed by figures within the U.S. and West Germany, the British government approached these nations with an offer to collaborate on the project and to seek contributions towards the cost involved. Following the acceptance of all three nations, on 22 May 1962, Hawker received a formal Instruction to Proceed with the procurement of materials for the construction of the nine aircraft. The nine aircraft were ordered as the "Kestrel FGA.1", which was essentially an improved version of the P.1127. On 7 March 1964, "XS688" became the first Kestrel to conduct its maiden flight, flown by Bill Bedford. The Kestrel had fully swept wings and a larger tail than the early P.1127s, and the fuselage was modified to take the larger 15,000 lbf (85 kN) Pegasus 5 engine as in the P.1127/Kestrel prototype "XP984", in addition to some other changes, such as addition of ultra high frequency (UHF) radio and assorted operational equipment in a bay house within the rear fuselage.