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A formation of De Havilland DH-4s, British-designed, American-built bombers of World War I.
The most efficient aircraft engine of the war, the American 12-cylinder, 400-horsepower, liquid-cooled Liberty. Standing beside it is Henry H. "Hap" Arnold, future Commanding General, U.S. Army Air Forces (USAAF).
niques and recommended the establishment of two air forces, one to support ground forces and another to launch independent strategic attacks against the sources of German strength. A dearth of aircraft and aircrews prevented the development of the latter effort, and the 1917 Bolling mission had given the idea lowest priority. American Expeditionary Force
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