Private First Class McKenna was a member of Company I, 3rd Battalion, 27th Infantry Regiment, 25th Infantry Division. He was seriously wounded by the enemy in North Korea on 6 June 1951 and returned to duty on 20 June 1951. He was listed as Missing in Action while fighting the enemy in Korea on 20 July 1951. He was presumed dead on 15 March 1954. His remains were not recovered. His name is inscribed on the Courts of the Missing at the Honolulu Memorial.

McKenna was awarded the Purple Heart with Oak Leaf Cluster, the Combat Infantryman's 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.