form of the Snecma Atar engine. During June 1951, the French Armée de l'Air (AdA) issued a detailed requirement for a jet-powered aircraft capable of functioning in several roles, including as a bomber, a low-level attack aircraft, or an all-weather interceptor. In response to this requirement, French aircraft manufacturer SNCASO decided to adapt its existing S.O. 4000 design so that it could perform the desired missions roles. During 1951, test flight of the S.O.4000 prototype had demonstrated promising performance for the type, supporting the decision to proceed with a further development of the design. According to aviation authors Bill Gunston and Peter Gilchrist, "It would be fair to claim that in the early 1950s the Vautour was the most promising twin-jet warplane in Western Europe". An initial order for three prototypes was placed by the AdA. On 16 October 1952, the first prototype of the revised design, which had been designated as the S.O. 4050, conducted its maiden flight. The flight test programme proceeded relatively smoothly; during one early flight, a prototype was recorded as having exceeded Mach 1 during a shallow dive. A follow-on order for six pre-production aircraft was soon received; one of these was powered by a pair of Armstrong Siddeley Sapphire engines while another was furnished with Rolls-Royce Avon engines, both British designs, while the remainder were powered by the French Atar engine. Subsequent production aircraft would use the Atar engine, having proven to be sufficiently mature and, with the aid of water injection, capable of sufficient power to enable the Vautour to take off while carrying a full payload. Production and further development Vautour II, the aircraft was manufactured in three distinct variants. During 1958, the aircraft entered service with the AdA; the Vautour would remain in use by the AdA for several decades. While the final French aircraft being retired from frontline service during 1979, a number were retained and soldiered on in various secondary duties into the early 1980s. The Vautour ultimately saw no combat usage during its service with the AdA; throughout the majority of its service life, the type was maligned as obsolete and relatively underpowered. Although it had been a moderately competent aircraft when it had been originally developed, the Vautour never benefitted from the adoption of sufficiently powerful engines, even though suitable powerplants did become available over time. As an interceptor, it was soon outclassed by the newer Dassault