Private Allen was a medic with the Medical Detachment, 2nd Engineer Combat Battalion, 2nd Infantry Division. He was taken Prisoner of War while tending his wounded comrades along the Chongchon River near Kunu-ri, North Korea, on 1 December 1950 and died while a prisoner on 28 February 1951.

Allen was awarded the Purple Heart, the Prisoner of War Medal, the Combat Medical 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.