 During 1964, production of the Galeb commenced, making it the first indigenously-developed jet aircraft to enter mass production in Yugoslavia (the first jet-powered plane built by Yugoslavia was the Ikarus 451M in 1952, which did not enter production).A ground attack-orientated derivative of the Galeb, named the J-21 Jastreb, was also developed shortly thereafter; aside from the strengthening of the airframe, one distinct difference between the two aircraft was the deletion of the rear cockpit on the J-21 Jastreb, this location has instead been covered by a fairing and the internal space used to contain avionics and other aircraft equipment.Beyond domestic adoption with the Yugoslav Air force, the Galeb achieved export sales as well; the Libyan Air Force was a prolific operator of the type; by 2002, it reportedly possessed a total of 80 aircraft remaining in its inventory.