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.

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.

Trinity remained there, inactive, until growing tension in both Europe and the Far East prompted the Navy to enlarge its building programs, and to recondition and recommission old ships.

Transferred to the Pacific Fleet early in 1939, Trinity carried oil to Dutch Harbor, Alaska, for use by the Coast and Geodetic Survey.

She departed Manila Bay on 28 February 1941 to commence the first of eight round-trip voyages in that year to ports in oil-rich Borneo and the Netherlands East Indies.

As war clouds gathered on the horizon in the summer of 1941, an organization plan was drawn up which designated Trinity as part of the Manila-based Task Force 2.

On 8 December, Trinity lay alongside the fuel docks at Sangley Point, discharging oil to the storage tanks ashore, when she received word from Admiral Thomas C. Hart that "Japan has commenced hostilities — govern yourselves accordingly."

Dropping anchor at the congested port of Tjilatjap, she remained there a week before Vice Admiral William A. Glassford, Commander, United States Naval Forces, Southwest Pacific (COMSOWESPAC), dispatched her to Iran to obtain refined fuel oil to relieve the critical fuel shortage in the war zone.

Departing Tjilatjap on 17 February in company with Edsall, she proceeded independently after her escort was ordered back to port and arrived at Abadan, Iran, on 9 March.

Attached to this command for the remainder of the year, Trinity plied the Milne Bay-Brisbane route, while also touching at Cairns and Townsville, Australia.

By January 1945, as the war progressed steadily towards the Japanese homeland, Trinity continued her unglamourous but vital job of plying the triangular New Guinea-Shouten Islands-Admiralty Islands route, shuttling cargoes of oil needed to keep the warships of the Fleet in operation.