Sangamon, one of twelve tankers built on a joint Navy-Maritime Commission design later duplicated by the T3-S2-A1 type, was laid down as Esso Trenton (MC hull 7) on 13 March 1939 by the Federal Shipbuilding and Dry Dock Co., Kearny, New Jersey. Launched on 4 November 1939 and sponsored by Mrs. Clara Esselborn. Operated by the Standard Oil Company of New Jersey on runs from gulf coast ports to the east coast and acquired by the U.S. Navy on 22 October 1940. Renamed Sangamon and designated a fleet oiler, AO-28, she was commissioned on 23 October 1940, Cmdr. J. R. Duncan in command.
- Navy Department, Office of the Chief of Naval Operations, Naval History Division: Dictionary of American Naval Fighting Ships, Volume VI