Hawker Siddeley Harrier cancelled after the release of the British Government's 1957 Defence White Paper, which advocated a policy shift away from manned aircraft and towards missiles. This policy resulted in the termination of the majority of aircraft development projects then underway for the British military. Hawker sought to quickly move on to a new project and became interested in Vertical Take Off/Landing (VTOL) aircraft, which did not need runways. According to Air Chief Marshal Sir Patrick Hine this interest may have been stimulated by the presence of Air Staff Requirement 345, which sought a V/STOL ground attack fighter for the Royal Air
Hawker Siddeley Harrier at of thrust and first ran in September 1959. A contract for two development prototypes was signed in June 1960 and the first flight followed in October 1960. Of the six prototypes built three crashed—including one during an air display at the 1963 Paris Air Show. In 1961 the United Kingdom, United States and West Germany jointly agreed to purchase nine aircraft developed from the P.1127, for the evaluation of the performance and potential of V/STOL aircraft. These aircraft were built by Hawker Siddeley and were designated "Kestrel FGA.1" by the UK. The Kestrel was strictly an evaluation aircraft and