Gloster's G.40, more popularly known by its Air Ministry Specification, E.28/39, like the earlier Heinkel He 178, was produced purely as a flight test bed for British turbojet development. The G.40, W 4041/G, Britain's first pure turbojet powered aircraft first flew on 15 May 1941, followed by the first flight of W 4046/G a year and nine months later, on 1 March 1943. Both aircraft were fitted with various Frank Whittle-designed engines, ranging from the earliest 850lb s.t. W. I to the later 1.526 lb s.t. Rolls-Royce W.2B123 and 1.700lb s.t. Power Jets W.21500. Top level speed reached by the short-lived second prototype is cited at 466 mph, this machine crashing on 30 July 1943, after spinning inverted from 37.000 feet. The pilot, Sqn. Ldr. Douglas Davie, bailed out safely.