built. Piaggio P.X R.C.15, 501–522 kW (670–700 hp) – 48 built. Piaggio P.IX R.C.40, 507 kW (680 hp) – 140 built. Alfa Romeo 126 RC.34, 582–671 kW (780–900 hp), also fitted to early versions of the SM.79. 58 built. In addition, one aircraft, the SM.81B, was built in a twin-engined configuration, powered by two 627 kW (840 hp) Isotta-Fraschini Asso XI inline engines and a streamlined, glazed nose. It had inferior performance to the three-engined versions and was not taken further. Fuel The fuel tanks, as was standard for Italian multi-engined aircraft, were metal self-sealing fuel tanks using materials developed by SEMAPE, the specialized manufacturer. Eight tanks were fitted, with six in the centre wing (4 × 150 L/40 US gallon and 2 × 1,140 L/301 US gal tanks) and two 370 L (100 US gal) tanks (or 780 L/210 US gal with Gnome-Rhône 14K engines) in the outer wings. This gave an overall fuel capacity of 3,620 or 4,400 L (960 or 1,160 US gal). Operational history The SM.81 first saw combat during the Second Italo-Abyssinian War, where it showed itself to be versatile serving as a bomber, transport and reconnaissance aircraft. SM.81s also fought in the Spanish Civil War with the Aviazione Legionaria and were among the first aircraft sent by the fascist powers to airlift aid to Francisco Franco. Despite their obsolescence, by 1940, when Italy became involved in World War II, around 300 (290–304 depending on source) SM.81s were in service with the Regia Aeronautica. The first Italian aircraft to enter action in East Africa were a pair of SM.81s. On 11 June 1940, one of them attacked Port Sudan and the other flew a reconnaissance flight over the Red Sea. That same night, three SM.81s took off to bomb Aden, but one turned back, and one of the other two hit a hill near Massawa while trying to land. A further flight was concurrently deployed against Anglo-Rhodesian defensive positions in British Somaliland immediately before the decisive Battle of Tug Argan, presaging a limited role as a tactical bomber. Its low speed and vulnerability to fighter aircraft meant that during daytime the SM.81 was restricted to second line duties, finding use as a transport. At night it was an effective bomber, particularly in the North African theatre. Anti-ship actions were also carried out, but without significant success. Most SM.81s were withdrawn by the time of the