Following shakedown, "Trinity" got underway from Chesapeake Bay on 11 February 1921, bound for the Mediterranean. She arrived at Valletta, Malta and delivered general stores for USS "Pittsburgh" (CA-4) before proceeding to Split, Yugoslavia (present-day Croatia), with fuel oil for American ships operating in the Adriatic. After a three-day layover at Split, she got underway on 8 March for Venice, where she arrived on 12 March. She eventually called at Pula (then in Italy, now in Croatia), before making port at Brindisi to take on fuel oil and general supplies for the naval base at Constantinople, Turkey, and American naval forces operating in Turkish waters. Following the delivery of this cargo, "Trinity" sailed to Gibraltar, then departed there on 4 April and arrived at Tompkinsville, Staten Island, New York, on 17 April. Subsequently based at Norfolk, Virginia and assigned to the Naval Overseas Transportation Service, the oiler operated along the United States East Coast and in the Caribbean until she was decommissioned on 22 December 1923 and laid up at the Philadelphia Navy Yard.