Professor FitzSimonds served for 27 years in the U.S. Navy as both a surface line officer and intelligence officer, retiring in 2001 with the rank of captain. His operational assignments included USS Blakely (FF-1072), USS Enterprise (CVN-65), and the USS America (CV-66) Battle Group. His ashore assignments included tours with the Chief of Naval Operations Current Intelligence Division, the Office of the Chief of Naval Operations Naval Warfare Directorate (OP-095), the Navy Operational Intelligence Center Detachment-Newport, the Chief of Naval Operations Strategic Studies Group, and the Net Assessment Directorate of the Office of the Secretary of Defense.