Armstrong's regular commission was terminated on February 25, 1952, and he became an ensign in the United States Navy Reserve. On completion of his combat tour with "Essex", he was assigned to a transport squadron, VR-32, in May 1952. He was released from active duty on August 23, 1952, but remained in the reserve, and was promoted to lieutenant (junior grade) on May 9, 1953. As a reservist, he continued to fly, with VF-724 at Naval Air Station Glenview in Illinois, and then, after moving to California, with VF-773 at Naval Air Station Los Alamitos. He remained in the reserve for eight years, before resigning his commission on October 21, 1960.