The rotary engine reduced rough the running and overheating of early air-cooled engines, namely. Disadvantages were gyroscopic forces, lubrication losses, low time-between-overhaul, air resistance to rotating cylinders, and limited rpm.

The first successful rotary engine is generally attributed to the American F.O. Farwell in 1896; but the French Gnome engine, developed by the Seguin brothers, was much more successful in bringing the rotary to a broad aviation market beginning in 1909. The original Gnome had two valves, with the inlet in the head of the piston and the exhaust in the in the cylinder head. The monosoupape, as the name signifies, had only one valve in the cylinder head, eliminating a weak feature of the earlier design, and was the most numerous model during World War I.

It powered the French Nieuport, Bleriot, and Pomier aircraft, the British Nieuport 28C.1 and Sopwith F.1 Camel, and was also built under license in England, Italy, and the U.S.