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 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 exact requirements also included a weight of 140,000 lb (64 t). The B.35/46 specification required that the fully laden weight would be under 100,000 lb (45 t), the bomber have a cruising speed of 500 knots (580 mph; 930 km/h) and that the service ceiling would be 50,000 ft (15,000 m). 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 American Strategic Air Command. In late 1948, the Air Ministry issued their specification B.35/46 for an advanced jet bomber that should be the equal of anything that either the Soviet Union or the Americans would have. The exact requirements included that the fully laden weight would be under 100,000 lb (45.36 t), the ability to fly to a target 1,500 nautical miles (1,700 mi; 2,800 km) distant at 500 knots (580 mph; 930 km/h) with a service ceiling of 50,000 ft (15,000 m) 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 10,000 lb (4,500 kg) and measuring 30 ft (9.1 m) in length and 10 ft (3.0 m) in diameter, could be accommodated. This request would be the foundation of the V bombers.
However, 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 435 knots (806 km/h) and a lower height over the target of 35,000 to 45,000 ft (11,000 to 14,000 m). 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 perspective 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 SA.4 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.