Laid down under Maritime Commission contract (MC hull 337) on 27 August 1942 as Cowpens by Sun Shipbuilding & Drydock Co. of Chester, Pennsylvania, the ship was launched on 21 December 1942, sponsored by Mrs. A. Poestrak.

After arriving at Adak on 30 June, she serviced ships both underway and in port, from 9 July until departing on the 14th to reload at San Pedro, California.

Between 30 August and 12 October, she made one voyage transporting oil from San Pedro to tanks ashore at Tutuila, Samoa, and at Espiritu Santo.

With an underway replenishment group, she refueled units of a fast carrier force headed by the Bunker Hill (CV-17) on 27 December.

On her third underway refueling assignment, her luck ran out as her group was located on 18 June by Japanese aircraft searching for escort carriers in the vicinity, and all three oilers were hit.

After three sorties from that port to fuel fleet units, she shifted her base to Kossol Roads, Palau, on 19 October in preparation for the amphibious invasion of the Gulf of Leyte in the Philippines.

Back at Ulithi on 23 March, Saranac resumed fueling fleet units there until getting underway on 1 April to support the invasion of Okinawa.

She rejoined the underway replenishment forces off Okinawa on 22 April and provided continuous services until sailing once again for Ulithi on 8 June.

At Alameda, California, she was stripped of all military equipment not required for the passage to Guam and fitted with power regulators and transformers.