Major Greis was a veteran of World War II. In Korea, Major Greis was a member of the 8202nd Army Unit, Korean Military Assistance Group (KMAG). He was taken Prisoner of War while advising the South Koreans in South Korea on 13 February 1951 and died while a prisoner on 23 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, Major Greis was awarded the Silver Star Medal, the Bronze Star Medal with 2 Oak Leaf Clusters, the Purple Heart, 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, the Republic of Korea War Service Medal and the World War II Victory Medal.