Gosper was named for a county in southern Nebraska. Oregon Shipbuilding at Portland launched her on 20 October 1944 under a Maritime Commission contract. Mrs. E. P. Nelson was the sponsor. The Navy took her over and commissioned her on 18 November 1944, with Commander F. W. McCann in command.
Supplies were loaded after she sailed for Seattle on 29 November, and on 6 December she was at San Francisco to hoist landing craft aboard. Shakedown off southern California and a set of amphibious exercises ended with a return to San Diego on 6 January 1945. Troops and stores then filled her for two passages to Pearl Harbor as the fleet drove west. The second arrival was 27 February. At Pearl Harbor she was altered into a casualty-evacuation transport and fitted with operating rooms and other hospital spaces. Okinawa was the operation she was to join. She left Pearl Harbor on 18 March, made Ulithi on 31 March, and entered Kerama Retto on 6 April. The first troops had gone ashore on nearby Okinawa five days earlier.
Suicide planes were over the anchorage through most of that day. Gosper brought down at least one. Also lost that day were Hobbs Victory, Logan Victory, and LST-447. She remained at Kerama Retto until 17 April, looking after men hurt in the fighting ashore, then continued to Ulithi and Guam. On 24 April the wounded went ashore at the naval hospital. At Saipan she embarked more than 1,000 reserve combat troops and sailed once more for Okinawa, arriving off the beaches on 1 May. Kerama Retto was her anchorage from then until 10 July. Casualties still came aboard, and she still helped beat off the air raids. On 10 July she moved to Buckner Bay, on Okinawa's east side, and joined a convoy bound for Ulithi, Pearl Harbor, and San Francisco. That last port was made on 7 August 1945.
Repair work was still going on when the war ended, and she was quickly assigned to carry occupation forces. She sailed on 26 August for the Philippines and anchored at Manila on 15 September. Hospital spaces were the reason a large party of American, British, and Canadian former prisoners came aboard, men who had been held on islands in Japanese hands, some of them since 1941. Pearl Harbor was the stop on their way to Seattle, where she arrived on 12 October. Magic Carpet duty followed. From a 26 October sailing at Seattle she made two round trips to Pearl Harbor with veterans, then on 8 February 1946 headed for the east coast by the Panama Canal. Newport News was the arrival, on 24 February. She was decommissioned on 10 April. The Maritime Commission took her back and berthed her on the James River with its defense reserve. One battle star was credited for the war.