In the early 1950s the British Air Ministry was faced with the very real threat to the Defence of the United Kingdom posed by high flying jet bombers delivering a nuclear strike. The Ministry felt that to counter such a threat there would be a requirement for an interceptor which could reach a very high altitude with sufficient speed to be able to manoeuvre into a position from where the nuclear bombers could be attacked, before they could deliver their nuclear payload. The obvious answer to this dilemma was of course to use a rocket engine, but the problem with this was that rocket powered aircraft (such as the German ME163 Komet and others experimented with by the Russians) always had a very short duration of powered flight. Once its fuel had been expended it could only be expected to glide back to its base. Hence the Air Ministry issued Operational Requirement 301, inviting a number of aircraft manufacturers to submit designs for a simple reusable aircraft employing a rocket for the main propulsion, but with a turbojet to get home. Designs were received from the Blackburn, Westland, Fairey Aviation, Saunders Roe, AVRO and Bristol aircraft companies to the Air Ministry specifications, and after due deliberations the Saunders Roe proposal was accepted for development, with the Avro design as its backup. The project was almost stillborn, for the 1952 Defence cuts almost saw the project axed, but somehow it survived, although with the number of prototypes cut from three to two. Saunders Roe produced a preliminary mock-up to evaluate the design in September 1953, but such a unique and revolutionary concept would require a great deal of development work. Thus it was not until the 16 May 1957 that the first prototype SR53 (XD145) took to the air on its maiden flight,This prototype going supersonic on the 15th May 1958 Meanwhile the English Electric company was working on a rocket powered project of its own, the English Electric F23/49, later to be developed into the supersonic English Electric Lightning jet fighter. The Royal Air Force was also having second thoughts on the desirability of rocket powered aircraft, for by that time, developments in turbojet engines design had resulted in these having a performance being only marginally (with the exception of the climb rate) less than that of a rocket. Another factor was the introduction of both the Bloodhound SAM missile and the ICBM which effectively made the original SR53 purpose obsolete. In December 1957 a serious setback occurred when the second prototype, piloted by test pilot, Squadron Leader John Booth who was killed in the accident, crashed and exploded at Boscombe Down having failed to take off in circumstances that were never fully explained. Even before this accident the SR53 project had been cancelled by the Defence cuts announced in the 1957 Government White Paper. The remaining prototype continued for a while as a test vehicle for satellite re-entry trials but its career as a fighter was effectively ended. This SR53 was finally retired to the aviation museum at RAF Cosford.