On 8 January 1945, "Ro-46" put to sea from Kure for her fourth war patrol, with a patrol area in the South China Sea west of Luzon. U.S. forces entered Lingayen Gulf and U.S. forces began their invasion of Luzon on 9 January 1945. On 29 January 1945, "Ro-46" torpedoed the attack transport at ; although "Cavalier" survived, she had to be towed to Leyte. reported sinking a fleet oiler from a convoy at 01:13 on 30 January 1945, then departed the area.