After being commissioned, "Steamer Bay" conducted trials and went on a shakedown cruise down the West Coast, before arriving at San Diego. On 14 May, she sailed for the New Hebrides, transporting Marine Air Group (MAG) 61. She arrived at Espiritu Santo on 30 May, where her cargo was unloaded. She departed on 2 June, arriving at San Diego on 20 June. On 19 July, she loaded 298 marines and 72 aircraft, and proceeded westwards for the Marshall Islands. She hence arrived at Majuro on 1 August, where she discharged her cargo. She headed for Pearl Harbor, where she was attached to the United States Third Fleet to store replacement aircraft to support the ongoing Mariana and Palau Islands campaign and the Philippines campaign. Seventy-two planes were loaded onto "Steamer Bay", and she sailed for Seeadler Harbor, Manus Island, arriving on 21 August. Throughout the next two and a half months, she remained on station, providing replacement aircraft and crew for Task Group 38. After completing her duties, she returned to Pearl Harbor, where she underwent repairs and training from 15 November to 5 December.