LeO founded by Fernand Lioré and Henri Olivier as agricultural and general engineers at Levallois-Perret (Paris) 1906, building first aircraft 1908. Lioré helped form Witzig-Lioré-Dutheuil aero engineers 1911, but formed Les Ateliers d’Aviation Lioré et Olivier 6 March 1912. Built designs by 15 early aviators. From 1914 built over 2,000 Morane-Saulnier monoplanes and nearly 3,000 Sopwith 1½-strutters. First major original design was LeO 4 recon biplane (September 1916), followed by post-war twin-engined 5, 3-engined 6 flying-boat and amphibian and 7 twin-engined bomber, 7/2 and 7/3 going into production. Four LeO 12s, one a passenger airliner, led to LeO 20, classic night bomber (February 1927), 311 delivered to Armée de l'Air plus 9 exported. Derived types were 21 18-passenger airliner, 21S ambulance for 10 stretchers and 214 trainer for 14 paratroops. Minor types included LeO 8 parasol monoplane night fighter (April 1923), LeO 9 low-wing fighter, H.180/193/194/197/198 single-engined flying-boats and amphibians and handful of licensed Ciervas. In 1930s LeO developed various single-engine biplanes, LeO 203/204/206 heavy bombers (4 x 350-hp in tandem pairs), LeO 300 giant bomber, various Cierva (Lepère-designed) autogyros, and tremendous variety of marine aircraft with prefix H, notably H.252-259 seaplanes derived from LeO 20, H.24 and 24-2 passenger flying-boats, H.43 shipboard observation seaplane, and H.47 and H.246 large 4-engined boats, designed for Air France but converted into ocean patrol bombers. Nationalization law transferred Argenteuil factory to SNCASE and Rochefort seaplane works to SNCASO. By far most important LeO was 45 twin-engined bomber (16 January 1937), outstanding aircraft, 1,783 ordered from SNCASE Clichy and Levallois plants, 452 delivered by collapse; Vichy government resumed production at SNCASE Ambérieu from April 1942, many LeO 451 used against Allies.