Harry Armstrong was commissioned in the Army Medical Corps in 1930 and was attached to the Air Corps in 1931. After serving in the Army Air Forces in World War II, he transferred to the U.S. Air Force when it became a separate branch of service in 1947. From 1949 to 1954 he served as the 2d Surgeon General of the Air Force. He retired in 1958 as a U.S. Air Force Major General.