Sergeant Thornton was a member of the 5th Cavalry Regiment, 1st Cavalry Division. He was seriously wounded by the enemy in South Korea on 19 August 1950 and returned to duty on 25 August 1950. He was seriously wounded again on 18 September 1950 and returned 20 September 1950. He was Killed in Action while fighting the enemy in North Korea on 2 November 1950.

Thornton was awarded the Purple Heart with 2 Oak Leaf Clusters, 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.