Sergeant First Class Mentzos was a member of Company I, 3rd Battalion, 21st Infantry Regiment, 24th Infantry Division. He was taken Prisoner of War while fighting the enemy near Chochiwon, South Korea on 12 July 1950, forced to march to North Korea on the "Tiger Death March", and died while a prisoner at An-Dong, North Korea on 3 July 1951 of beriberi and malnutrition. His remains were not recovered. His name is inscribed on the Courts of the Missing at the Honolulu Memorial.

For his leadership and valor, Sergeant First Class Mentzos was awarded the Bronze Star Medal, the Purple Heart with 2 Oak Leaf Clusters, the Combat Infantryman 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.