The single seat Hunter prototype first flew in 1951 to finally enter RAF service in 1954. Nearly 2,000 Hunters were built, being considered the most successful jet fighter built in Great Britain, serving with numerous air forces around the world. The Hunter was developed by Hawker Aircraft to meet a RAF requirement for a day interceptor fighter to replace the Venom and Meteor. The single seat swept wing fighter was powered by the new 7,500 Ib thrust Rolls-Royce Avon jet, being armed with four 30 mm Aden guns in a detachable under fuselage gun pack. The prototype flew in July 1951, and the F.1 entered service in July 1954, with 139 being built by Hawkers at Kingston and Blackpool between May 1953 and October 1954. The F.2 was built in smaller numbers by Armstrong Whitworth and was powered by an Armstrong Siddeley Sapphire jet as a safeguard against problems with the Avon. The F.4 flew in the autumn of 1954 being an improvement over the short range F.1, carrying more fuel and underwing stores, and after replacing the F.1's based at home it was issued to RAF squadrons in Germany. Armstrong Whitworth produced the equivalent F.5 which was again powered by the Sapphire. Hawkers then developed the improved F.6 which was ordered in quantity by the RAF having a more powerful 10,000 lb thrust Avon for improved performance and it could carry four underwing fuel tanks, bombs or rocket projectiles. These were delivered from May 1955 to replace the F.4's and F.5's in service, and continued in service until replaced by Lightning F.2's from the end of 1962. This version of the Hunter was regarded as a real pilots aircraft, which was a joy to fly. To replace Venoms as ground attack fighters, Hawker's developed the FGA.9 from the F.6, having provision for more underwing stores, larger drop tanks and a tail parachute. Aircraft were modified from F.6's, serving the RAF between January 1960 and December 1971.