Humphreys volunteered for assignment to the Aeronautical Division, U.S. Signal Corps and was chosen to replace Benjamin Foulois in pilot training by the Wright brothers. On October 26, 1909, after three hours of instruction by Wilbur Wright, he became the first Army aviator to solo in a heavier-than-air craft, and thus the first pilot of the first progenitor of the United States Air Force. The Army's sole military airplane crashed on November 5, 1909, after which Humphreys returned to the Corps of Engineers.