Assigned to the Pacific Fleet, "Monongahela" departed Norfolk in November 1942 for Aruba, Netherlands West Indies, where she loaded oil and then steamed to Nouméa, New Caledonia, via the Panama Canal to supply American forces engaged in the struggle for Guadalcanal. For the next year, the tanker shuttled fuel oil, aviation gasoline, diesel oil, various dry cargoes, and ammunition between San Pedro, California, and Allied supply bases in the Solomons, New Caledonia, and New Zealand as part of the long seaborne pipeline supplying fuel for victory in the South Pacific. In January 1944, following a stateside overhaul and a Pearl Harbor fuel run, the big auxiliary joined the 5th Fleet support group for the invasion of the Marshall Islands, supplying various ships and small bases at Kwajalein, Eniwetok, and Majuro as those atolls were captured during the campaign.