While serving with the 170th Infantry, Bullard was seriously wounded in action in March 1916 at the Battle of Verdun. After recovering, he volunteered on October 2, 1916, for the French Air Service () as an air gunner. He was accepted and underwent training at the Aerial Gunnery School in Cazaux, Gironde. Following this, he went through his initial flight training at Châteauroux and Avord, and received pilot's license number 6950 from the Aéro-Club de France on May 5, 1917. Like many other American aviators, Bullard hoped to join the famous squadron Escadrille Americaine N.124, the Lafayette Escadrille, but after enrolling 38 American pilots in the spring and summer of 1916, it stopped accepting applicants. After further training at Avord, Bullard joined 269 American aviators at the Lafayette Flying Corps on November 15, 1916, which were a designation rather than a unit. American volunteers flew with French pilots in different pursuit and bomber/reconnaissance aero squadrons on the Western Front. Edmund L. Gros, who facilitated the incorporation of American pilots in the French Air Service, listed in the October 1917 issue of "Flying", an official publication of the Aero Club of America, Bullard's name is on the member roster of the Lafayette Flying Corps.