He joined the
Lafayette Flying Corps of the
French Air Service in 1917. In June of the following year, he joined the
United States Air Service. Henry Gibson recalled that Putnam approached him at his tent and said, "I am going across the seas to get in the big fight." He did indeed, by way of a cattle boat, and joined the French Foreign Legion on May 31, 1917. He was transferred to the air service and trained at
Avord. Putnam was assigned to Escadrille SPA 94 on 12 December 1917, and was posted to SPA 156 on 7 February 1918. While with the latter unit, he shot down four planes before being transferred to SPA 38 on 1 June 1918, where he claimed two more planes shot down. He was discharged in June 1918. When the United States entered the war, Putnam joined the
United States Army Air Service as a first lieutenant and briefly assumed command of the 134th Aero Squadron before joining the 139th Aero Squadron as a flight commander. As a gesture of respect, his aviators gave him a dinner in Paris, all 150 under his command. Wine was to be served and he abstained from alcohol, to which end he turned over his glass, and the others followed suit. With the 139th, Putnam scored his last three victories before he was killed in action. He wrote to Henry Gibson, director of Camp Becket-in-the-Berkshires, where Putnam had been a camper and counsellor, "Can you imagine anyone falling 20,000 feet, nearly four miles, smashing a machine to kindling wood and only getting a broken tooth out of it all? No! Well, I am afraid you are going to try, for that is just what I did yesterday morning." ==Death==