The Harrier GR1 has been considerably developed since entering service with RAF No.1 Squadron in April 1969. GR3, T4 and GR5 variants have all seen RAF service, and the GR7 and T10 are now on the front line. The Sea Harrier entered service with the Royal Navy in 1979, and played a large part in the 1982 Falklands conflict. Harriers are also in service with the United States Marine Corps and the Spanish and Italian forces. This is a history of the aircraft, much of it contributed by Duncan Simpson, the Harrier's Chief Test Pilot.