The Saunders-Roe SR.53 was a British prototype interceptor aircraft of mixed jet and rocket propulsion developed for the Royal Air Force (RAF) by Saunders-Roe in the early 1950s. As envisaged, the SR.53 would have been used as an interceptor aircraft, using its rocket propulsion to rapidly climb and approach incoming hostile bombers at high speeds; following its attack run, the aircraft would then return to its base using jet propulsion.
Although the SR.53 proved to have promising performance during test flights, the requirement for such an aircraft had been overtaken by rapid advances in surface-to-air missile technology, leading to reconsideration of the aircraft's purpose. In July 1960, the development programme was formally cancelled, by which time a total of 56 test flights had been performed. A pair of prototype SR.53 aircraft had been completed and used during flight tests. The second prototype was destroyed during one such test flight in June 1958. The first prototype has been preserved to this day. It rests on public display at the Royal Air Force Museum Cosford.
Design and development
Background
The Second World War had demonstrated the importance of strategic bombing to modern warfare, and as the emerging Cold War developed, the development of new and more effective air defences against large waves of hostile bomber aircraft armed with nuclear weapons became a priority for many nations. During the war, Nazi Germany had extensively developed its own rocket-powered aircraft to augment its interception capabilities, in the final two years of the war, it had been able to deploy aircraft such as the Messerschmitt Me 163 and Bachem Ba 349 which, via rocket propulsion, had been capable of unparalleled rates-of-climb, enabling them to (at least in theory) rapidly sortie to intercept enemy bombers before they reached their targets. As the performance of these aircraft had become increasingly well known to the Allies, RAF experts were eager to explore and understand the underlying technology.
In the aftermath of the war, German rocket technology was studied extensively by various members of the former Allied nations. Britain had quickly opted to commence a programme to develop liquid-propellant rockets with the aim of boosting aircraft during the take-off phase, known within the RAF as rocket-assisted take-off gear (RATOG), and during the climb-to-altitude phase of flight. In 1946, work began on a pair of new British-built rocket motors, the de Havilland Sprite with a maximum thrust of and the Armstrong Siddeley Snarler with of thrust; these rocket motors made use of different propellants, the Sprite used a high-test peroxide (HTP) monopropellant while the Snarler harnessed a methanol/water/liquid oxygen mix. During the early 1950s, both engines proceeded to the flight testing phase; however, some of the demand for their role to provide fighters with increased performance was soon being met by the increasing prevalence of conventional jet engines being equipped with reheat instead.
In May 1951, faced with reports on the increasingly potential capability of, and thus the threat posed by, the growing Soviet strategic bomber fleet and that nation's newly developed atomic weapons, the British Air Ministry proceeded to draft an Operational Requirement, OR 301, which sought a rocket-powered interceptor that could attain an altitude of in just 2 minutes 30 seconds. Many of the performance requirement laid out by OR 301 was due to the anticipation of rapid increases in performance by the opposing Soviet aircraft; by the early 1960s, it was suspected that these bombers might well be capable of supersonic speeds of up to Mach 2 with a potential operational altitude as high as . Accordingly, a capable defence interceptor that could form part of the nation's measures to counter this threat would need to be capable of similar speeds and an exceptionally high rate of climb in order to reach high altitude bombers in time.
The development of the Sprite and the Snarler had led to the possibility of a more powerful rocket engine being developed as the planned powerplant for a viable "point defence" interceptor. The requirements of O.R. 301 were considered onerous, including a ramp launch and landing on a skid, and with the compliance of the companies which had approached to tender, the amended Specification F124T allowed for a mixed powerplant configuration along with the adoption of a conventional undercarriage. On 21 February 1951, the revised Specification F124T was circulated to half a dozen of Britain's various aircraft manufacturers to solicit their submissions.