After shakedown, "Marvin H. McIntyre" stood out of Los Angeles Harbor, 18 January 1945, on her first war mission. She arrived at her destination, Lunga Point, Guadalcanal, 4 February and commenced intensive amphibious training operations in preparation for the invasion of Okinawa. Departing the Solomons 15 March, "McIntyre" steamed in convoy for the advanced staging area at Ulithi. There she rendezvoused with her task unit and sailed for the Ryukyus 27 March. At Okinawa on 1 April, she discharged passengers and cargo for the initial attack. The attack transport remained off Okinawa until 5 April, when she retired to the Marianas with wounded marines as passengers. She arrived at Saipan on the 9th, debarked the casualties, and got underway against the next day for Pearl Harbor.