In 1943, he was drafted into the Army Corps of Engineers, Fort Belvoir, Virginia, where he was first in the camouflage unit and later the unit assigned to produce technical manuals. Life magazine used his field guide principles for a plane-spotting manual; later the Air Corps used them in their training manual for plane identification. Once, he persuaded a drill sergeant to reroute marching troops so as to avoid a horned lark's nest.