These engines powered the majority of aircraft in the first half of the war, both Allied designs as well as German examples produced by Motorenfabrik Oberursel.

Sold under the French translation, the Gnome was a single-cylinder stationary engine of about 4 hp (3 kW) that ran on kerosene (known in the UK and South Africa as paraffin) intended to be used in industrial applications.

More than 1,700 of these engines would be built in France, along with license-built models in Germany, Sweden, Britain, the United States, and Russia.

Léon Lemartin and Jules Védrines were two young engineers who participated in the design, development, and implementation of the Omega, and in the milieu of the pioneering days of flight they both went on to become successful pilots.

Early models used two valves, one in the cylinder head and a second embedded in the piston itself, counterweighted to open at the end of the stroke.

Without any springs or pushrods, the valve would pop open on the downstroke, allowing fuel to be drawn into the cylinder from the crankcase area.

Gnome also tried a 14-cylinder two-row version, the Double Lambda of 160 hp (120 kW), but this saw little use, even though it was copied by Oberursel as the U.III in Germany, and used in a few early Fokker fighter designs without success.

Like Gnome, the Le Rhône designs were widely licensed, in this case the 110 hp Le Rhone 9J was produced in Germany by Oberursel as their Ur.II model as designated by IdFlieg, and in the United States; the Union Switch & Signal Company of Swissvale, PA was reported to have produced some 10,000 units - it was also built in Austria, Britain and Sweden.

The ultimate development was the 250 kW (340 hp) double row Le Rhône 18E of 1917 based on 9R components, however like all multi-row rotaries, it suffered from unresolvable cooling problems and was never used operationally.

The Gnome rotaries started becoming less common on front line aircraft after 1916 as power advances failed to keep pace with either liquid-cooled V-8 engines, or even the more advanced conventionally valved rotaries, such as the 104 kW (139 hp) Clerget 9Bf, and they peaked with the 120 kW (160 hp) Monosoupape 9N, however they remained popular for training aircraft.

The 9C and 9J were the most commonly used engines for early and mid-war designs both in French and British service and was also used for fighters in Germany where Oberursel had taken out a license just before the war.

To provide more power Gnome once again turned to the two-row solution, using two banks of 7 cylinders, delivering the 625 hp (460 kW) Gnome-Rhône 14K Mistral Major in 1929.

Leaving the idea of having many engines in a single "K-series", Gnome continued work with the basic mechanical design to produce the 18-cylinder two-row Gnome-Rhône 18L of 1400 hp (1030 kW).

The original 14N-0/1 was run through a number of versions, the 14N-10/11 being used on the Bloch MB.210 bomber, the 14N-25 on early examples of the MB.152 fighter, and the 14N-49 on late MB.152s as well as LeO 451s and Amiot 351s.

With the fall of France in 1940, Gnome et Rhône was ordered to produce the BMW 801 under license, while the 14M and 14N saw limited use on some German designs, such as the Henschel Hs 129B, Gotha Go 244B, and Messerschmitt Me 323.

Another air raid by Lancasters of 617 Squadron led by Wing Commander Leonard Cheshire had also severely damaged the Limoges factory on 8/9 February 1944.

With the end of the war, the company was in no condition to continue in the aero-engine business, although they picked up small contracts to produce M4 Sherman tanks for the French army.

[citation needed] From 1920 Gnome et Rhône diversified into the bicycle and motorcycle business producing some relatively successful and stylish products.