 Following her shakedown cruise, "Tappahannock" reported for duty with Commander, Service Force, Atlantic (ComServLant), on 13 August, and soon got underway south for Panama.In the Canal Zone, the oiler took on board 300 tons of stores for Motor Torpedo Boat Squadron (MTBRon) 3, as well as two PT boats, and left Balboa on 29 August, bound for the South Pacific

"Tappahannock" unloaded her cargo at Nouméa, New Caledonia, on 18 September; and then visited Auckland, New Zealand; Pago Pago, Samoa; and Nadi, Fiji, before becoming station tanker at Nouméa.There, she fueled a wide variety of ships until 20 November, when she headed for the west coast.