In March 1944, "Monongahela" joined the At-Sea-Replenishment Group for Fast Carrier Task Force 58, for the remainder of the war operating continuously with the fast carriers, participating in every major central Pacific operation from the Hollandia, New Guinea, invasion in April 1944 to the invasion of Okinawa a year later. The oiler supported the flattops during the second strikes on Truk, the invasion of the Marianas, the Battle of the Philippine Sea, the Palaus invasion, the Leyte campaign, and the liberation of the Philippines. In November 1944, she was one of those oilers in Capt. Jasper T. Acuff's At-Sea-Refueling Group that made the perilous run through Surigao Strait into the East China Sea to refuel Admiral William F. Halsey's 3rd Fleet/TF 38 during its raids on the Indochinese and China coasts. The ship also supported the invasions of Iwo Jima and Okinawa, narrowly escaping damage from suicide air attacks at Kerama Retto, on 16 April 1945. At the end of the Okinawa operation in June, "Monongahela" steamed to San Francisco for a much needed overhaul which was still in progress when hostilities ceased on 15 August.