Santos is a career submariner, with at-sea operational submarine assignments aboard USS Tinosa (SSN 606), USS Miami (SSN 755), USS Virginia (SSN 774) and USS Nevada (SSBN 733). During these tours, Santos conducted deployments to the North Atlantic, Mediterranean, South America, Pacific and Arabian Gulf, including combat operations in support of operations in Kosovo and Iraq. Ashore, he has served as a nuclear engineering instructor; a submarine strike officer during the initial stages of Operation Iraqi Freedom; a member of the Joint Staff, J-3, Deputy Directorate for Global Operations; and in the strategy branch of the Office of the Chief of Naval Operations Naval Warfare Integration Group.