Corporal Shackelford was a member of Company B, 1st Battalion, 24th Infantry Regiment, 25th Infantry Division. He was taken Prisoner of War while fighting the enemy along the Kum River, South Korea, on 14 July 1950, forced to march to North Korea on the "Tiger Death March" and died while a prisoner during the march from Manpo to Chunggang-jin, North Korea, on 2 November 1950. His remains were not recovered. His name is inscribed on the Courts of the Missing at the Honolulu Memorial.

Shackelford was awarded 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.