Prior to his academic career, McDowell had a long career with the United States Army and government agencies. After graduating from Texas A&M University (then known as the Agricultural and Mechanical college of Texas) and the Officer Candidate School at Fort Benning, Georgia, he was commissioned Second Lieutenant of Infantry in the U. S. Army. After commissioning, McDowell was assigned to teach in the Army Specialized Training Program (ASTP) at Fort Benning. He then attended the Basic Airborne Course at Fort Benning, and, after completion, was assigned to the 82nd Airborne Division and the 11th Airborne Division. He also served with the 97th Infantry Division in Europe. His early assignments included command positions from platoon leader to battalion commander. As part of the 82nd Airborne Division, McDowell participated in Operation Market Garden, jumping behind enemy lines and engaging objectives in Nijmegen and Arnhem.