The Short SA.4 Sperrin (named after the Sperrin Mountains) was a British jet bomber design of the early 1950s, built by Short Brothers and Harland of Belfast. It first flew in 1951. From the onset, the design had been viewed as a fall-back option in case the more advanced strategic bomber aircraft, then in development to equip the Royal Air Force's nuclear-armed V bomber force, experienced delays; the Sperrin was not put into production because these swept-wing designs, such as the Vickers Valiant, were by then available.
As their usefulness as an interim bomber aircraft did not emerge, a pair of flying prototypes were instead used to gather research data on large jet aircraft and to support the development of other technologies, such as several models of jet engines. The two aircraft completed were retired in the late 1950s and ultimately scrapped sometime thereafter.
Development
The Air Ministry issued a specification on 11 August 1947 B.14/46 for a "medium-range bomber landplane" that could carry a "10,000 pound [4,500 kilogram] bomb load to a target 1,500 nautical miles [2,780 kilometres] from a base which may be anywhere in the world", with the stipulation it should be simple enough to maintain at overseas bases. The requirements also included a weight of . This request would become the foundation of the Royal Air Force's V bombers, Britain's airborne nuclear deterrent.
At the same time, the British authorities felt there was a need for an independent strategic bombing capability—in other words that they should not be reliant upon the United States Strategic Air Command. In late 1948, the Air Ministry issued their specification B.35/46 for an advanced jet bomber that would serve as a successor to the Avro Lincoln, the then-standard heavy aircraft of RAF Bomber Command, and that it should be the equal of anything that either the Soviet Union or the United States would have. The exact requirements included that the fully laden weight would be under , the ability to fly to a target distant at with a service ceiling of and again that it should be simple enough to maintain at overseas bases. A further stipulation that a nuclear bomb (a "special" in RAF jargon), weighing and measuring in length and in diameter, could be accommodated. This request would be the foundation of the V bombers.
The Air Ministry accepted that the requirement might prove to be difficult to achieve in the time-scale required and prepared for a fall-back position by re-drafting B.14/46 as an "insurance" specification against failure to speedily develop the more advanced types that evolved into the Vickers Valiant, Avro Vulcan and Handley Page Victor, as this was to be a less ambitious conventional type of aircraft, with un-swept wings and some sacrifice in performance. The only significant performance differences between B.14/46 and the more advanced B.35/46 were a lower speed of and a lower height over the target of . According to aviation authors Bill Gunston and Peter Gilchrist, the specification's ignorance of a swept wing was odd for the era, and had been made in order to allow the prospective bomber to be delivered more quickly.
A total of four firms submitted tenders to meet the B.14/46 specification, Shorts' submission was selected as it had been judged to be superior. The selection of Shorts was "astonishing" according to Bill Gunston and Peter Gilchrist, and noted that their submission, while being a sound design, had apparently been subject to luck. Under this requirement, the Air Ministry placed a contract for two flying prototypes and a static airframe with Shorts. The design was known initially by the company designations of S.42 and SA.4; the aircraft would later receive the name "Sperrin".
As the Sperrin was considered to be a possible production aircraft early on, a decision was taken for the two prototypes to be constructed upon production jigs; this served to slow their construction. Bill Gunston and Peter Gilchrist commented that, if a subsequent production order had been issued, an initial operational squadron could have been equipped by late 1953.