Private First Class Tannehill was a member of Company L, 3rd Battalion, 27th Infantry Regiment, 25th Infantry Division. He was seriously wounded by the enemy in Korea on 14 September 1950 and returned to duty on 25 September 1950. He was listed as Missing in Action while fighting the enemy in Korea on 6 November 1950. He was presumed dead on 31 December 1953. His remains were not recovered. His name is inscribed on the Courts of the Missing at the Honolulu Memorial.

Tannehill was awarded the Purple Heart with Oak Leaf Cluster, the Combat Infantryman Badge, 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.