engine were located in the wing section between the fuselage and tail booms, and integral fuel tanks were fitted. The armament initially consisted of one nose mounted Hispano-Suiza Akan m/41A and four Akan m/39AA autocannons, two in the wings, and two in the nose. On the A-2 the guns were replaced with belt fed Bofors Akan m/45. The J 21A-3 (later designated A 21A) could carry rockets and bombs. Later in the Saab 21's service life the autocannons were rebarreled to fire American ammunition due to economics. These improved firing performance but the Saab 21 was now only viable as a ground attack aircraft due to the rate of change in fighter design. Three prototypes were completed of which only two were to be flyable, while the third was a static airframe for stress testing purposes. On 30 July 1943, the first J 21 prototype conducted its maiden flight, flown by SAAB test pilot Claes Smith. During takeoff, he used too much flap, impairing acceleration and climb. This resulted in it hitting a fence and damaging the undercarriage, although he was able to land successfully afterwards. Further development During 1945, several options were explored to improve the 21's performance. During the first half of the year, the company was working on a variant that would be powered by a Rolls-Royce Griffon engine to give the 21 a projected top speed of . Other projects, such as the Saab 27 were also designed for the Griffon, however all work on piston-engine upgrades was abandoned by the end of the year. In parallel with these studies, SAAB and other Swedish companies had been evaluating the adoption of jet propulsion. Two early studies, designated as RX 1 and RX 2, were twin-boom aircraft similar to the 21. Swedish Air Force enthusiasm for a jet fighter in late 1945 pushed SAAB to produce a version of the J 21 using jet propulsion. At Swedish Air Force request, existing J 21 aircraft were converted to jet propulsion in 1947 and redesignated J 21R. This required modifications to over 50 per cent of the airframe, including the tailplane and wing. The aircraft was to be powered by a single British-sourced de Havilland Goblin turbojet engine, to replace the DB 605B. It entered Swedish Air Force service as their first jet aircraft. Operational history The first example from the first batch of 54 of the first production