Castro joined the faculty in 2013 after serving 33 years in the U.S. Army, where he obtained the rank of colonel. Castro began his military career as an infantryman in 1981. He served in a variety of research and leadership positions, including as director of the Military Operational Medicine Research Program, Headquarters, U.S. Army Medical Research and Materiel Command, Fort Detrick, Maryland. Castro has completed two tours in Iraq, as well as peacekeeping missions to Saudi Arabia, Bosnia and Kosovo.