THIS MONOGRAPH, written by Mrs. Juliette A. Hennessy of the USAF Historical Division, recounts the development of aviation in the United States Army from April 1861, when the Army first became interested in balloons as a means of observation, to April 1917, when America entered World War I. The origins and organizations of the Army's air arm are told in detail, with particular emphasis on early air force personnel, planes, and experiments. In the process the monograph traces the early development of what today is The United States Air Force. Of necessity, the monograph tends strongly toward the chronological variety. This is owing to several factors, the thinness of aviation activities for most of the long period covered and an equal thinness in records being the principal factors. Only a few books which deal with this early period of Army aviation have been written, and all of them together do not cover the period. This, then, is the first attempt to put the story into a single volume. Because the story of the air arm from April 1917 to the beginning of World War II also has not been fully covered it is expected that the present monograph will be the first of three, which, when completed, will become the basis for a published history of the Army Air Arm, 1861-1939. Like other Historical Division studies, this history is subject to revision, and additional information or suggested corrections will be welcomed.