During the interwar period in the 1920s and 1930s, Corlett commanded various army detachments. He graduated from the U.S. Army Command and General Staff School at Fort Leavenworth, Kansas, in 1923 and the U.S. Army War College in Washington, D.C., in 1925. He was an instructor at the United States Army Coast Artillery School and at U.S. Army Command and General Staff School. He was a member of the General Staff of the War Department from 1934 to 1939. While he was there he was promoted to lieutenant colonel on February 1, 1936. He commanded regiments in Hawaii, California, Washington, and Alaska from 1939 to 1941. He was promoted again, now to the temporary rank of colonel, on June 26, 1941, but just three months later he was further promoted, now to the general officer rank of brigadier general, on September 30.
