Following the Armistice in 1918, Maj. Gen. Mason M. Patrick, Chief of Air Service, American Expeditionary Forces, directed that a record be made of lessons learned during the war. This information, he believed, was needed for planning the Air Service of the future. The reports prepared by commanders, pilots, observers, and other members of the various Air Service units in response to General Patrick's directive are of considerable historical interest for the information they contain about the Air Service and its employment at the front. A select group of the reports on lessons learned make up Part I of this volume of World War I documents on U. S. military aviation. Part II is devoted to a report on the effects of Allied bombing in World War I. This long-forgotten document, the result of a post-war investigation by the Air Intelligence Section of General Headquarters, American Expeditionary Forces, is the counterpart of the well-known United States Strategic Bombing Survey of World War II. This volume is the last in a series that the Office of Air Force History is publishing on the U. S. Air Service in World War I.