Etablissments LeO of Levallois-Perret was founded by Henri Olivier and Fernand Liore. Established as agricultural and industrial engineers in 1906, entered aviation 1908. Liore worked with Witzig-Liore-Dutheuil in 1912. Firm built Morane-Saulnier types before and during First World War, producing over 2,000. From 1916 built Sopwith 1-Strutter.
In 1921 started up airline Aeronavale (Societe Maritime de Transport Aeriens), and in 1922 began design and construction of civil and military flying-boats and bombers. An airliner derived from the 1924 bomber served Air Union. Four engined flying-boats developed up to Second World War. Cierva autogiros built under license. LeO 451, built 1939-1940, was best French bomber of period and used for research after war. The Argenteuil factory became part of SNCASE and the Rochefort plant part of SNCASO in 1936.