He returned to the United States in August 1917, four months after the American entry into World War I, and served (now with the rank of captain) with the 58th Infantry Regiment in Pennsylvania and North Carolina. In July 1918, his regiment was transferred to the Western Front to serve as part of the American Expeditionary Force (AEF), commanded by General John J. Pershing, who had led the Pancho Villa Expedition. As an infantry officer, he participated in the Champagne-Marne defensive operations, the Aisne-Marne Offensive, the Battle of Saint-Mihiel and the Meuse-Argonne Offensive. The war ended soon afterwards, after the Armistice with Germany was signed on November 11, 1918. For his bravery in the war he was awarded the French Croix de guerre.