The Hawker P.1127 and the Hawker Siddeley Kestrel FGA.1 were the experimental and development aircraft that led to the Hawker Siddeley Harrier, the first vertical and/or short take-off and landing (V/STOL) jet fighter-bomber. Kestrel development began in 1957, taking advantage of the Bristol Engine Company's choice to invest in the creation of the Pegasus vectored-thrust engine. Testing began in July 1960 and by the end of the year the aircraft had achieved both vertical take-off and horizontal flight. The test program also explored the possibility of use upon aircraft carriers, landing on HMS Ark Royal in 1963. The first three aircraft crashed during testing, one at the 1963 Paris Air Show.