America's major technological contribution to World War I was the "Liberty" aircraft engine. It was light, powerful and efficient. America's auto industry turned out 20,478 of them for the war. The Liberty engine continued in military and civilian use even into World War II.
This 12-cylinder, liquid-cooled 443-hp Liberty 12-B demonstrates the Army Air Service engineers' quest for higher flight and more efficient power. Its turbosupercharger allowed aircraft to reach great heights by compressing the thin air at high altitudes to preserve engine power. A turbosupercharger uses engine exhaust to power an air compressor, which in turn feeds dense, oxygen-rich air to the engine. A sturdy circular arrangement of reduction gears on this particular engine (called "epicyclic" gears, in the round silver case around the propeller shaft) allowed the propeller to turn at variable speeds for better performance. This method of changing the propeller's thrust by shifting gears eventually gave way to adjusting the angle or pitch of the propeller blades instead.
These kinds of experimental refinements were carried out at McCook Field and Wright Field, the Army Air Service's testing facilities near Dayton, Ohio. The tests led to greater knowledge and better aircraft in the 1920s and 1930s and paved the way for developing the superior aircraft the Allies would need in the Second World War.