Recalled to the colors just before America's entry into World War I, Sumner was commissioned a first lieutenant on 22 March 1917 and sailed on 5 August 1917 for duty in France. He served with the 81st Company, 6th Machine Gun Battalion. While in France, he was promoted to captain.
Leading his troops during the advance on Tigny on 19 July 1918, Capt. Sumner was killed in action by German shellfire. He was buried in the field, and France awarded him the Croix de guerre, posthumously.
