Based on the successful Galeb combat-capable trainer, the SOKO J-21 Jastreb (Hawk) is an all purpose single-seat light attack aircraft built for the Yugoslav air force. The J-21 is superficially quite similar to the Galeb, with the same unswept wing configuration with wingtip tanks which gives them both a remarkable resemblance to the Lockheed T-33. Nevertheless, the J-21 is equipped with a more powerful version of the Rolls-Royce Viper engine which allows for superior performance figures and a necessarily heavier armament load. Besides the basic attack versions, the Jastreb also functions as a reconnaissance aircraft and a trainer, all of which are combat-capable, and has also been exported to Libya and Zambia. Yugoslavian J-21s saw combat during the Bosnia and Kosovo Wars and today remain in service with the air forces of Serbia, Croatia and Bosnia-Herzegovina.

The first prototype of the Jastreb flew on May 1961 with deliveries to the Yugoslav air force beginning four years later. The basic attack version is designated J-21 and is used exclusively in its country of origin, foreign models being known as the J-21E. Reconnaissance versions featured cameras in the lower fuselage and tip tanks and had two weapons hardpoints removed although they were still capable of ground attack. Yugoslav versions were designated RJ-21 and export versions RJ-21E. Finally, a two-seat trainer is known as the TJ-21 used exclusively by Yugoslavia.