After serving as a Medical Officer in World War II, Maxwell Steel left active duty and returned to Philadelphia where he was appointed chief hospital resident at the Memorial Hospital. In 1947 he began post-graduate training in internal medicine at the Graduate School of Medicine, University of Pennsylvania. In 1947 he received a Regular commission in the U.S. Army and was assigned in 1948 as a resident in internal medicine at Walter Reed General Hospital, Washington, D.C., which he completed in June 1950. He transferred to the Air Force in July 1949 and retired in 1975 as a U.S. Air Force Major General.