Commissioned as hostilities in Europe and Asia began to draw the United States ever closer to the conflict, Mattole was assigned to duties in the North Atlantic.

Mattole returned to New York 10 January 1943, continued to Norfolk and then to Bermuda where she underwent intensive exercises in fueling at sea, antisubmarine, and antiaircraft procedures.

Arriving in the Netherlands West Indies on the 26th, she carried oil to Guantanamo Bay and underwent fueling exercises before taking up duties as station tanker at Port of Spain, Trinidad, 20 July.

With only one interruption, she continued this essential duty sailing to Guantanamo Bay; New York; Portland, Maine; and Argentia, Newfoundland, until mid‑1945 when she extended her operations to include gulf coast ports.

The single break in this assignment came in November 1944 when she was ordered to accompany an extremely slow convoy of landing craft and tugs towing Army barges to Cherbourg, France.