McDowell joined the University of Texas at Arlington (then Arlington State College) in 1959 as Assistant Professor of Military Science and Tactics. After being promoted to lieutenant colonel, he left the university to serve on the Joint Chiefs of Staff, where he was intelligence officer of the Airborne Command Post, a job that often involved flying with the President of the United States and his senior staff to evaluate foreign military threats and provide mobile control of U.S. nuclear forces. In this role, McDowell was the custodian of the Nuclear Football, which is used by the President of the United States to authorize the use of nuclear weapons while away from fixed command centers.