The Hawker Siddeley P.1154 was a planned supersonic vertical/short take-off and landing (V/STOL) fighter aircraft designed by Hawker Siddeley Aviation (HSA). Development originally started under P.1150, which was essentially a larger and faster version of the basic layout and technology being developed by the smaller subsonic Hawker Siddeley P.1127/Kestrel. A key difference of this design was the addition of plenum chamber burning, essentially an afterburner-like arrangement in the thrusters used during hover, greatly increasing their thrust. The release of NATO Basic Military Requirement 3 for a VTOL strike-fighter led to widespread industry participation. Hawker felt the P.1150 did not meet the requirements, so it was enlarged to become P.1150/3, and then renamed P.1154. This Mach 2-capable aircraft was the technical winner of the eleven submissions for NBMR-3, with the Dassault Mirage IIIV selected as a second design. Political infighting between the two groups and their various supporters, along with continual changing of the strategic environment, led to neither project progressing into production. Meanwhile, Hawker Siddeley considered modifying the airframe for a joint specification for an aircraft by the RAF and Royal Navy. Between 1961 and 1965 the two services harmonised their specifications to preserve design commonality. However, the RAF's desired configuration was to take precedence over that of the Royal Navy's. A number of proposals were submitted; at one stage, a twin-Spey design was considered, then rejected. Following the Labour government's coming to power the project was cancelled in 1965. The Royal Navy would acquire the McDonnell Douglas F-4 Phantom II, while the RAF continued to foster development of the P.1127 (RAF), leading to the successful Harrier family. Development Background During the late 1950s, Hawker Siddeley Aviation (HSA) was keen to develop a new generation of combat aircraft that would be capable of supersonic speeds. Unfortunately, despite repeated attempts to revive the program, the in-development Hawker P.1121 fighter would ultimately be left unfinished, principally due to a lack of a political support for development following the release of the 1957 Defence White Paper by Minister of Defence Duncan Sandys. Recognising the need to promptly commence work on another development program, HSA's chief aircraft designer Sir Sydney Camm, who had been in regular discussions with Sir Stanley Hooker of Bristol Aero Engines, decided that the company should investigate the prospects of developing and manufacturing a viable combat-capable vertical take-off and landing (VTOL) fighter aircraft. Bristol Aero Engines and Hooker had already