Corporal Hannan was a Light Weapons Infantryman with Company K, 3rd Battalion, 35th Infantry Regiment, 25th Infantry Division. He was taken Prisoner of War while fighting the enemy in North Korea on 28 November 1950 and died while a prisoner on 30 April 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, Corporal Hannan was awarded the Bronze Star Medal, 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.