The SAAB 21 was a Swedish fighter and attack aircraft designed and manufactured by Swedish aviation company SAAB. It used a relatively unorthodox and visually distinctive combination of a twin boom fuselage and a pusher configuration, giving the aircraft a unique appearance.
Work on the development of the 21 commenced at SAAB following a decision by the Swedish Air Force to embark on a large-scale expansion programme in preparation to fears that the nation might get dragged into the Second World War. The company designed a monoplane twin-boom aircraft, powered by a single Daimler-Benz DB 605B engine that was positioned within the rear of the fuselage, directly behind the pilot, that drove a rear-facing propeller, commonly known as a pusher configuration. This arrangement allowed armaments to be contained within the aircraft's nose section as well as providing the pilot with a high degree of external visibility. To safely enable the pilot to bail out without striking the propeller behind him, it was decided to adopt an ejection seat.
On 30 July 1943, the 21 performed its maiden flight; on 1 December 1945, the first model of the fighter, the J 21A-1 was introduced to service. It was quickly followed by the improved J 21A-2, which featured a heavier armament arrangement, and the B 21A-3, which was a dedicated fighter-bomber mode of the type. In response to interest from the Swedish Air Force in adopting a jet-powered fighter, SAAB developed a conversion of the aircraft, using the British de Havilland Goblin as its powerplant. The jet-powered model of the aircraft was designated as the 21R. During the mid-1950s, less than ten years after its introduction, the 21 was withdrawn from service, having been replaced by a new generation of jet-powered fighters such as the de Havilland Vampire and the Saab 29 Tunnan,