The Gnome Monosaupape was a rotary 9 cylinder single valve engine developing 80 100 horsepower originally designed in 1913 and produced through WWI.
Described by Thomas Sopwith as one of the major engine design improvements to that time, it was used in many aircraft of the day. Monosaupape was French for single valve. This single valve system was operated bu a single cam and pushrod system and worked off the crankshaft eliminating dozens of small parts and most engine failures.
These engines and their direct descendants were installed in many British aircraft of World War 1 and helped the allies attain higher reliability of their aircraft. The engine was produced in numbers through WWI by the Gnome Engine Company later called Gnome et Rhone. The English also produced under license these engines in England in a 7 and 9 cylinder version and the 9 cylinder in two different displacements.
This engine had a direct effect on the War for the allies by reducing substantially the losses of aircraft and pilots due to engine failure and insuring that more aircraft could be ready for missions instead of being hanger babies using up limited resources of parts and mechanics.