The ship was built by the Kaiser Shipyard in Vancouver, Washington, and launched on 9 November 1944, sponsored by Mrs. Walter E. Hanawalt, and was accepted by the Navy and commissioned on 1 December 1944.

Following a shakedown cruise off the California coast, Saint Croix departed San Diego on 31 January 1945, bound for the South Pacific.

She then made three trips to New Guinea to bring more troops, debarking at Manila on 17 June, and at San Fernando on 14 July and 8 August.

Next, she loaded marines at Guam in late September and delivered them to Tsingtao, China, on 11 October as part of Operation Beleaguer.

She then sailed to Hai Phong, Indochina (via Manila), to embark Chinese troops for passage to Kaohsiung, Formosa with USS Napa.