variant, the J 21A-1 was delivered to the Swedish Air Force on 1 December 1945. Construction was at SAAB's main plant in Trollhättan and deliveries of this model ran until 5 December 1946, when deliveries of two batches totalling 124 of the J 21A-2 began. A third order, in two batches totalling 119 of the A21A-3 fighter-bomber completed production of the piston-engine variants. A total of 298 J 21As were constructed prior to the production line ending in 1948. During December 1945, the Svea Wing (F 8) became the first fighter unit to receive the J 21. During the following year, other units of the Swedish Air Force, such as Göta Wing (F 9), also began to receive the type. However, within less than four years, some squadrons were already being re-equipped with a new generation of jet fighters capable of far greater speed, such as the de Havilland Vampire. Despite the original intention for the type to be principally used in air defence roles, in service, the J 21 was utilized mainly in the light bomber role. The type was used only by the Swedish Air Force. Officials doubted its effectiveness due to its unconventional design. In response, the Swedish Air Board requested that SAAB study a development with the engine in the nose as the J 23. This aircraft used the J 21's DB 605B engine and had a more traditional appearance, similar to the North American P-51 Mustang, but its projected performance was reduced, which became a key factor in improving the J 21 instead. The Swedish Air Force became interested in jet propulsion and from 1945, SAAB began studying modifications of the airframe to accommodate a jet engine in place of its piston engine. Production of the piston-engine version continued until 1948 while examples of the new jet engine version began being converted on the line. As a result of the conversions, the piston-engine powered J 21A began being retired in 1954. Variants J 21A-1 First production series of fighter version. 54 built between 1945 and 1946, retired in 1949. J 21A-2 Second and third production series of fighter version (62 aircraft each built between 1946 and 1947). Aircraft had better avionics and was armed with a Swedish gun. Retired between 1953 and 1954. J 21A-3 (later designated A 21A) First and second production series of attack version (66 aircraft each built between 1947 and 1949).