High Quality Content by WIKIPEDIA articles! The Saab 21R was a Swedish twin-boom fighter/attack aircraft made by SAAB. It was a jet-powered development of the piston-engined Saab 21 and is unusual for being the only airframe that saw service as both a piston-engined fighter, and a jet fighter. As a fighter, its service designation in the Swedish Air Force was J 21R, and saw service in the late 1940s.