Hawker Siddeley P . 1154 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 ) . Developed alongside the subsonic and smaller Hawker Siddeley P . 1127 / Kestrel , the P . 1154 was derived from the P . 1150 . The P . 1150 proposal did not meet NATO Basic Military Requirement 3 and , consequently , the P . 1154 was born . This Mach 2 - capable platform retained plenum chamber burning previously designed for the P . 1150 . Although the technical winner out of eleven submissions , follow - on testing and production for the P . 1154 did not proceed as a result of political strife . Meanwhile , HSA 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 in 1965 , the project was cancelled . The Royal Navy would acquire the F - 4 Phantom , while the RAF continued to foster development of the P . 1127 ( RAF ) , leading to the successful Harrier family . Development . NATO requirements . In 1961 , during the development of the V / STOL P . 1127 and Kestrel , HSA considered the feasibility of a supersonic V / STOL aircraft . This was influenced by a general perception at the time that supersonic aircraft held significantly more value than subsonic aircraft . Consequently , on 13 April 1961 , HSA decided to conduct preliminary work on a supersonic P . 1127 under the guidance of Ralph Hooper . The aircraft , designated " P . 1150 " and 50 % larger than the P . 1127 , would employ plenum chamber burning ( PCB ) – essentially an afterburner in the previously cold forward nozzles – in the engine . The engine was a Pegasus development named the " BS . 100 " , and had four swivelling exhaust nozzles . The front nozzles were equipped with PCB , which uses the same principle as an afterburner , allowing the aircraft to theoretically reach speeds of Mach 1 . 7 – 2 . The design effort was initially undertaken to cater for NATO Basic Military Requirement 3 ( NBMR . 3 ) , which was issued in August 1961 . Specifications called for a supersonic V / STOL strike fighter with a combat radius of . Cruise speed was to be Mach 0 . 92 , with a dash speed of Mach 1 . 5 . The aircraft , with a payload , had to be able to clear a obstacle following a takeoff roll . However , as requirement specifications changed , the aircraft was considered undersized ; subsequent studies confirmed these fears , and so Bristol enlarged the original PCB engine and raised the exhaust heat to increase thrust to 146 . 8 kN ( 30 , 000 lbf ) . A new larger design emerged , initially named " P . 1150 / 3 " before being redesignated the " P . 1154 " . NBMR . 3 also attracted ten other contenders , among which was P . 1154 ' s principal competitor , the Dassault Mirage IIIV . This design employed a separate lift / thrust engine concept whereby eight Rolls - Royce engines would provide lift , with a single Turboméca Atar for thrust . The Mirage IIIV was supported by British Aircraft Corporation . HSA submitted its design to NATO through the Ministry of Aviation ( MoA ) on 8 January 1962 and , in May that year , the P . 1154 emerged as the winner in the competition for the NBMR . 3 over the Mirage IIIV . The P . 1154 was judged to be technically superior , however the Mirage was politically palatable due to the cooperative development and production across member nations . The project was terminated in 1965 after the French government subsequently withdrew following the selection of the P . 1154 over the Dassault design . RAF and Royal Navy requirements . On 6 December 1961 , before the design was submitted to NATO , it was decided that the P . 1154 would be developed with the requirements for use by both the RAF and the Royal Navy . In February 1962 , the Royal Navy ' s Admiralty received the aircraft concept with great interest as the Royal Navy was seeking a new interceptor aircraft for their aircraft carrier s . As a single aircraft , the P . 1154 would replace Hawker Hunter s of the RAF and the de Havilland Sea Vixen s of the Fleet Air Arm ( FAA ) . However , the services sought different characteristics in their aircraft – the RAF desired a single - seat fighter with secondary intercept capability , while the Royal Navy wanted a two - seat interceptor capable of secondary low - level strike capability . Although financially and politically committed to a joint requirement with the Royal Navy , the RAF ' s single - seat design took precedence over the two - seat version of the Royal Navy . However , RAF P . 1154s would have to accommodate the Navy ' s large airborne intercept ( AI ) radar . When HSA submitted the design on 8 August , the Royal Navy criticised the proposal , which had a tandem undercarriage layout incompatible with catapult operations ; consequently , a tricycle undercarriage design was investigated and accepted as practical . In December that year , Rolls - Royce offered a PCB - equipped vectored thrust twin - Spey design as an alternative . This was seen as inferior , however , and was not considered in great detail . The aircraft required PCB for vertical takeoff , but this caused significant ground erosion . The aircraft would have been armed with the Red Top missile . With the RAF and Royal Navy requirements diverging , the aircraft ' s development started to stumble . While modifications towards naval requirements had been made , by July 1963 weight gain had become a considerable issue , and the Navy was openly criticising the choice of V / STOL . However , despite a stated Navy preference for a swing - wing fighter , on the 16 July 1963 the services agreed that the aircraft would be completely common , with the exception of different radar systems . By August 1963 Hawker Siddeley was expressing the view that range of changes made were damaging the aircraft ' s potential for export . At the same time , the Navy stated that it regarded the P . 1154 as a second - rate interceptor , and the RAF openly decried the loss of strike performance . By October 1963 , the MoA was concerned with the project ' s progress , and noted that the effort to combine a strike aircraft and a fighter in a single aircraft , and trying to fit that same airframe to both of the services , was " unsound " . Disfavour and cancellation . In November 1963 , the RAF still found the P . 1154 to be a suitable platform , while the Royal Navy appeared to consider the McDonnell Douglas F - 4 Phantom II a better fit for its needs . In response , Hawker Siddeley focused its efforts on the RAF version . On 26 February 1964 , it was announced in the House of Commons by the Conservative government that a development contract had been placed for the P . 1154 , equipped with the BS . 100 engine , as an RAF strike aircraft . At the same time it was announced that the Naval requirement would be met by Spey - engined Phantoms . More positive news emerged in 1964 ; on 30 October the BS . 100 engine ran for the first time and Hawker Siddeley received favourable reports that the P . 1154 was competitive with the performance of other aircraft , including the F - 4 Phantom II . However , on 2 February 1965 , the incoming Labour government , led by Harold Wilson , cancelled the P . 1154 on the grounds of cost , along with several other aircraft such as the BAC TSR - 2 strike aircraft and Hawker Siddeley HS . 681 VSTOL transport . At the time of cancellation , at least three prototypes were under construction . Following the cancellation , the RAF and Royal Navy adopted the F - 4 Phantom II instead , but the government also gave a contract for continued work on the P . 1127 ( RAF ) , which led to the Harrier ; this name had originally been reserved for the P . 1154 should it enter service . In retrospect , aviation author Tony Buttler considered the cancellation of the aircraft to be justified , noting the time consuming and expensive failures of attempts by other nations ( such as Soviet / Russia ' s Yak - 41 and West Germany ' s EWR VJ 101 ) at a supersonic VTOL aircraft .