With the entry of the U.S. in World War I, Rattner was recruited to join the U.S. Army's camouflage section by that unit's commanding officer, Homer Saint-Gaudens, son of sculptor Augustus Saint-Gaudens (Behrens 2009). He was sent to France, where he was "promoted to sergeant, put in charge of camouflage research, and served at the front in the Second Battle of the Marne, Château-Thierry, Belleau Wood, and on the Hindenberg Line. He received a severe back wound which troubled him for the rest of his life" (Culkin 1980).