Corporal Lennon was a member of Company A, 1st Battalion, 7th Cavalry Regiment, 1st Cavalry Division. He was seriously wounded by the enemy in North Korea on 4 June 1951 and returned to duty on 6 June 1951. He was seriously wounded again on 5 October 1951 and died of those wounds later that day.

Lennon 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.