Corporal Flanagan was a member of Company I, 3rd Battalion, 5th Infantry Regimental Combat Team. He was wounded by the enemy in South Korea on August 25, 1950 and returned to duty the following day. He was listed as Missing in Action while fighting the enemy near Tosong-Kogae, North Korea on April 23, 1951. He was presumed dead on December 31, 1953. His name is inscribed on the Courts of the Missing at the Honolulu Memorial.