Sergeant Sumpter was a member of Company C, 1st Battalion, 19th Infantry Regiment, 24th Infantry Division. He was taken Prisoner of War while fighting the enemy at the Rum River in South Korea on 16 July 1950, forced to march to North Korea on the "Tiger Death March", and died in his sleep at Apex Prisoner of War Camp in North Korea on 17 November 1950. His remains were not recovered. His name is inscribed on the Courts of the Missing at the Honolulu Memorial.

Sumpter was awarded the Purple Heart, the Combat Infantryman Badge, the Prisoner of War Medal, the Korean Service Medal, the United Nations Service Medal, the National Defense Service Medal, the Korean Presidential Unit Citation and the Republic of Korea War Service Medal.