The Hawker/Bristol funded P.1127 development began in 1957. The Bristol Pegasus engine (originally with only 11,000 lb thrust) was developed for the aircraft with heavy US funding support. It was based on the earlier Orpheus engine, and had a bifurcated jetpipe and vectoring front and rear nozzles. The P.1127 made its first hover on 21 October 1960 on tethers, but this was not considered to be beneficial to feel out the aircraft response, so the first untethered hover was made less than a month later, on 19 November 1960. First conventional flight was made on 7 July 1961 and first double transition on 12 September 1961. Control power was low about all axes, which, combined with suck-down and limited height control power, resulted in a high pilot workload in hover. Hot gas ingestion was overcome with a low forward speed in takeoff and landing. One of the two initial test aircraft crashed, with the pilot ejecting safely. The British government began supporting the development before the first flight, funding the first two prototypes, and later four more. Pegasus 3 power was increased to 13,500 lb thrust. In 1962, the UK, US and Germany initiated a tripartite program, funding nine improved P.1127 Kestrels for use by a UK-led tri-national squadron which conducted operational trials. These used Pegasus 5 engines, with thrust increased to 15,500 lb. The Kestrel paved the way for the Harrier (#21) .