Corporal Mayo was a member of Battery B, 503rd Field Artillery Battalion, 2nd Infantry Division. He was listed as Missing in Action while fighting the enemy near Kunu-ri, North Korea on December 1, 1950. He was presumed dead on March 12, 1954. His remains were not recovered. His name is inscribed on the Courts of the Missing at the Honolulu Memorial. Corporal Mayo was awarded the Purple Heart, 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.