 In 1937, Mendenhall was appointed an instructor in history at Yale University, promoted to assistant professor in 1942, and then to associate professor in 1946.He served additionally as assistant to the provost at Yale from 1943 to 1950; director of foreign area studies (1944–1946); director Office Teacher
Training (1958–1959), and Master of Berkeley College (1950–1959).from 1951 to 1952, he became the first occupant of the academic chair at the United States Naval War College that in 1953 would be named and carry the title of Ernest J.