During 1942, the Regia Aeronautica required a defence fighter to provide a defence against bombers accelerating the advance of Allied troops into Italy. The SM.91 was created, a twin-engine fighter with DB 601 engines, armed with six 20 mm MG 151s up front and a turret equipped with a 20 mm MG 151 controlled by the gunner. 2 were created, taking flight for the first time on 11 May 1943, and achieved 27 hours of flight time but never entered official evaluations. One was captured by the Germans, while the other was destroyed by Allied bombing raids.

Introduced in Update 1.85 "Supersonic", the SM.91 looks like a normal heavy fighter with a very good frontal armament capable of destroying an enemy aircraft or a light or medium tank very easily with a single burst, however the performance of the aircraft allows it to recover quickly enough when it loses a lot of speed, unlike other heavy fighters. In addition to this, it equips a small rear turret with a 20 mm cannon with which you can easily defend yourself from enemy fighters.