Corporal Koeppel was a member of Company C, 140th Medium Tank Battalion, 40th Infantry Division. He was listed as Missing in Action while fighting the enemy in North Korea on 13 June 1952. He was presumed dead on 18 March 1954. His remains were not recovered. His name is inscribed on the Courts of the Missing at the Honolulu Memorial.

For his leadership and valor, Corporal Koeppel was awarded the Bronze Star Medal, the Purple Heart, 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.