The regiment organized and trained in the United States at Camp Doniphan, Oklahoma and then shipped out for France where it began training under British tutelage in June 1918. In July, the 140th had its first taste of combat in the Gérardmer sector in the Vosges Mountains, where they conducted raids on German forces. They were moved to the Saint-Mihiel sector in September where they served as a reserve for the First Army. The regiment soon participated in the Meuse-Argonne offensive, the largest battle the American Expeditionary Forces waged during the war. After five days of intense battle, they were relieved by elements of the 1st Division and were placed in the Sommedieue sector where they launched harassing attacks on the enemy positions until the Armistice of November 11, 1918, ended the war. They were deactivated in 1919 with the rest of the 35th Division.