Lieutenant Colonel Diaz was a veteran of World War II. In Korea, he was a member of the 8202nd Army Unit, Korean Military Assistance Group (KMAG). He was taken Prisoner of War while advising the South Korean 14th Army in South Korea on 13 February 1951 and died of malnutrition and dysentery at Suan Bean Prison Camp on 30 April 1951. His remains were not recovered. His name is inscribed on the Courts of the Missing at the Honolulu Memorial.

For his leadership and valor, Lieutenant Colonel Diaz was awarded the Silver Star Medal, the Bronze Star Medal with Oak Leaf Cluster, 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.