Sergeant Allen was a member of Company C, 1st Battalion, 24th Infantry Regiment, 25th Infantry Division. He was seriously wounded by the enemy in South Korea on 6 September 1950 and returned to duty on 10 October 1950. He was taken Prisoner of War while fighting the enemy along the Chongchon River near Kunu-ri, North Korea, on 28 November 1950 and died while a prisoner on 31 March 1951. His remains were not recovered. His name is inscribed on the Courts of the Missing at the Honolulu Memorial.

For his leadership and valor, Sergeant Allen was awarded the Bronze Star Medal, Purple Heart with Oak Leaf Cluster, the Combat Infantryman's 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.