Sergeant Calkins was a Light Weapons Infantryman with Company I, 3rd Battalion, 35th Infantry Regiment, 25th Infantry Division. He was seriously wounded by the enemy in South Korea on 14 September 1950 and returned to duty later that day. He was listed as Missing in Action while fighting the enemy north of Ung-dong, North Korea on 28 November 1950. He was presumed dead on 31 December 1953. His name is inscribed on the Courts of the Missing at the Honolulu Memorial.

For his leadership and valor, Sergeant Calkins was awarded the Bronze Star Medal with Oak Leaf Cluster, 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.