In World War I many French and other Allied aircraft flew with Gnome, Le Rhône, Clerget and Bentley rotary engines, the ultimate examples of which reached 250 hp (190 kW) although none of those over 160 hp (120 kW) were successful. By 1917 rotary engine development was lagging behind new inline and V type engines which by 1918 were producing as much as 400 hp (300 kW), and were powering almost all of the new French and British combat aircraft.