A key feature of the aircraft is its geodetic airframe fuselage structure, which was principally designed by Barnes Wallis. Development had been started in response to Air Ministry Specification B.9/32, issued in the middle of 1932, for a bomber for the Royal Air Force. This specification called for a twin-engined day bomber capable of delivering higher performance than any previous design. Other aircraft developed to the same specification include the Armstrong Whitworth Whitley and the Handley Page Hampden. During the development process, performance requirements such as for the tare weight changed substantially, and the engine used was not the one originally intended. The Wellington was used as a night bomber in the early years of the Second World War, performing as one of the principal bombers used by Bomber Command. During 1943, it started to be superseded as a bomber by the larger four-engined "heavies" such as the Avro Lancaster. The Wellington continued to serve throughout the war in other duties, particularly as an anti-submarine aircraft. It holds the distinction of having been the only British bomber that was produced for the duration of the war, and of having been produced in a greater quantity than any other British-built bomber. The Wellington remained as first-line equipment when the war ended, although it had been increasingly relegated to secondary roles. The Wellington was one of two bombers named after Arthur Wellesley, 1st Duke of Wellington, the other being the Vickers Wellesley. Number built: 11,461 For more details including the 42 variants, click here. Rear fuselage showing geodetic construction.