The first prototype (designated "VX158") had a running length of 102.2 feet, a wingspan of 109 feet, and a height of 28.5 feet. Empty weight reached 72,000lb and this was against a gross weight of rating of 115,000lb. Power was from 4 x Rolls-Royce "Avon" turbojet engines. Performance included a maximum speed of 565 miles-per-hour, a cruising speed of 500 miles-per-hour, a service ceiling up to 45,000 feet, and a range out to 3,860 miles.
All proposed armament was to be held in an internal bomb bay, this to consist of a formidable collection of conventional drop bombs or a single "Blue Danube" nuclear air-dropped bomb - a war load of at least 20,000lb was estimated (though never fitted in testing).
Prototype VX158 originally appeared with RR Avon RA.2 series turbojets of 6,000lb output power and achieved its first-flight on August 10th, 1951. However, because sound progress on the project that would begat the Vickers Valliant was being had, the Sperrin project was officially cancelled by authorities - though it was allowed to continue in an experimental sense. This additional work then led to a second prototype, "VX161", being added to the program. The VX161 made it to the air for the first time on August 12th, 1952 and differed in being powered by RR Avon RA.3 turbojets of 6,500lb thrust each.
VX158 was eventually given a single de Havilland "Gyron" turbojet for testing and this unit was fitted in place of the original, lower portside Avon engine in the existing nacelle - though the increased size of the engine now forced an increase in the size of this particular nacelle as a result. In this guise, the bomber project went into the air for the first time on July 7th, 1955 and the experimental configuration continued testing the arrangement into the early part of the following year. Later in 1956, the aircraft took on a pair of de Havilland "Gyron" Gy2 series engines for additional flight-testing work - these units rated at an impressive 20,000lb of thrust each and paired with the existing Avon turbojet units per nacelle (the Gyron engines were given the lower position in each nacelle). A first-flight in this revised configuration then followed on June 26th, 1956.
Meanwhile, prototype VX161 continued along its own development timeline and was flown over the public during Farnborough 1956. It survived into 1957 by which point it was dismantled and officially scrapped. Prototype VX158 continued to test its various experimental engine configurations into 1958 before it, too, was given up for good.
Meanwhile, the V-bombers went on to have useful service lives for the RAF and took on more conventional roles beyond nuclear deterrence before the end (despite the fact that all three were accepted to fulfill the same over-battlefield role to begin with). This left the Sperrin as nothing more than a footnote in the V-bomber program.
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