 Nelson entered the Navy in 1967 and spent a short time at Naval Hospital, Corpus Christi, Texas, then served as senior medical officer at the Naval Ammunition Depot, McAlester, Oklahoma.He also served as a medical officer at Naval Hospital, Bremerton, Washington, and Head of the Occupational Medicine Branch, Bureau of Medicine and Surgery in Washington, DC.After an assignment with the Navy Environmental Health Center in Cincinnati, Ohio, he returned to Bremerton as the Director of Occupational and Environmental Health Services and Fleet Liaison Team coordinator for the Naval Regional Medical Center.