The original single Bristol Siddeley Orpheus-engined Fiat G91 was designed in accordance with NATO requirements for a standard lightweight tactical strike fighter to equip its forces. The first of three prototypes and 27 pre-production aircraft flew on 9 August 1956. Original production models included the G91R/1 photographic-reconnaissance version (three Vinten 70mm cameras) and similar R/3 and R/4 with armament changes; G91N modified aircraft to evaluate navigational aids; G91T/1 tandem two-seat version for advanced training at tran-sonic speeds, and similar T/3 and T/4 with equipment changes.

The G91Y is a twin-engined development of the G91 based upon the G91T version. Two prototypes were built (the first flying on 27 December 1966) followed by 20 pre-series G91Y for the Italian Air Force. Delivery of the initial series of 35 production aircraft to the Italian Air Force began in September 1971, as single-seat light tactical strike-reconnaissance fighters. Armament comprises two 30mm DEFA cannon and cameras in nose; four underwing attachment points for 450kg bombs, 340kg napalm tanks, 7 X 50mm rocket packs, 28 X 50mm rocket packs or 4 X 127mm rocket containers. G91 are in service with the air forces of the German Federal Republic (G91R/3 and G91T/3 - including R/3 licence-built in Germany), Italy (G91R/1, R/1A, R/1B, G91T/1 and G91Y) and Portugal (G91R/4).