Still in Shanghai at the beginning of the Pacific War on 8 December 1941, "Izumo" captured the American river gunboat and assisted in sinking the British river gunboat . On 31 December, the cruiser struck a mine in the Lingayen Gulf while supporting Japanese forces during the Philippines Campaign. She was towed to Hong Kong in February 1942 for repairs. "Izumo" was re-classified as a 1st-class cruiser on 1 July. She returned to Japan in late 1943 and was reclassified as a training ship for the Kure Naval District.