Though U.S. Army and Navy pilots predominantly used foreign equipment n their months of combat during World War I, American industry made a sizeable contribution to the war effort in the production of the Liberty engine. A testament to old-fashioned American ingenuity, the Liberty engine was designed in a Washington hotel room in just one week during May 1917, with testing beginning in July. The definitive version was the Liberty 12 (12 indicating the number of cylinders), efficient in the fact that it weighed only two pounds per horsepower. A total of 20,478 examples were produced by a host of familiar automobile makers that transitioned their assembly lines to aviation during the war. Liberty 12s endured after the cessation of hostilities, powering the NC-4 flying boat in its epic May 1919 transatlantic flight and the F-5Ls that formed the backbone of the Navy's immediate postwar scouting squadrons.