After graduation from the Naval Academy in 1920, Vice Admiral Wellborn served in the USS New Mexico (BB-40) and USS Nevada (BB-36), then in the USS West Virginia (BB-48) as aide and communications officer, Commander Battleships, followed by similar service in the USS California (BB-44). In 1933 he served three years at BuOrd, then returned to sea as CO of the USS Perry (DD-340). He later was navigator in the light cruiser USS Concord (CL-10) and gunnery officer for ComCruBatFor in the Honolulu (CL-48).
During World War II, Wellborn first served as Commander Destroyer Division 16, involved in amphibious landings in Sicily, and then with the Fifth Amphibious Force in the Pacific. After a tour as Director of Officer Personnel at BuPers, he assumed command of the USS Iowa (BB-61), participating in the first landing and occupation of Japan in 1945. Later highlights in his naval career included: Chief of Staff to CinCPac; Commander Second Fleet, Commander Eastern Sea Frontier; and Chairman of U.S. Delegation, UN Military Staff Committee.