Neshanic was built as the SS Marquette, ex MC hull 519 under Maritime Commission contract by the Bethlehem Shipyard, Inc., Sparrows Point, Maryland.

Following shakedown, Neshanic cleared Hampton Roads in convoy on 20 April 1943, and sailed for Aruba, Netherlands West Indies, whence she steamed, on the 27th, with a full cargo of petroleum products, for the Pacific to join the vital chain supplying American forces fighting in the Solomons.

She arrived at Nouméa, New Caledonia, delivered part of her cargo, and then continued on to the New Hebrides to discharge the remainder at Espiritu Santo and Efate.

After a brief respite at San Pedro, Neshanic returned to Pearl Harbor, underwent training exercises, and on 22 January 1944 set out to supply the fuel needed for the Marshalls' campaign.

On 31 January, Marines and Army troops landed on Kwajalein and Majuro atolls, while Eniwetok came under attack by the fast carrier group.

Between the 7th and 18th, she completed a replenishment trip to the Ellice Islands and then steamed to Kwajalein where she served as station tanker, at Roi, until departing for Pearl Harbor on 6 March.

Refueling the fast carriers twice before heading back to Hawaii, she procured another cargo at Pearl Harbor and immediately sailed west again, to Eniwetok.

A minute later, however, a 100 lb (45 kg) bomb landed on her cargo deck, aft on the starboard side, amongst drums containing lube oil.

On that date she sailed for Ulithi, proceeding from there to Saipan, from which she sortied on 21 February to resupply the forces engaged in fighting in the Iwo Jima area.

At Ulithi when the war ended, on 14 August she conducted one more underway replenishment mission from that base before departing for Tokyo Bay on 21 September.