During 1947, SAAB began converting the piston-engined J 21s to jet propulsion resulting in 64 J21Rs, with the type seeing service in the late 1940s and early 1950s before being replaced by a new generation of fighters designed from the start with jet propulsion, such as the DH Vampire and the Saab 29 Tunnan. Unfortunately, all original J21R aircraft were scrapped after retirement in the late 1950s, however, in the 1990s a group of volunteers took the surviving derelict Saab J21A airframe 21286, and rebuilt it into a J21R for display at the Flygvapenmuseum.

To gain experience with jet aircraft, ahead of the Saab 29 Tunnan project, Saab converted four Saab J21As with jet engines, to become J21R. Unfortunately, no J21R aircraft were saved after the type was retired at the end of the 50s. The museums J21A 21286 had no engine and was chosen to be rebuild as a J21R. The aircraft was handed over to the museum on 13 April 1998 as a J21R.

This machine is actually a surviving J21A, 21286, modified to represent the extinct jet variant. 64 J21Rs were originally constructed and they were soon converted to A21R attack aircraft.

Saab's J21R jet fighter retained the long legs of the J21A propeller plane, and compared to the otherwise rather similar Vampire it seems to stand twice as high! This machine is actually a surviving J21A, 21286, modified to represent the extinct jet variant. 64 J21Rs were originally constructed and they were soon converted to A21R attack aircraft.