The division was originally activated from Hawaii garrison units during World War II, slightly more than a month before the Japanese Attack on Pearl Harbor began the Pacific War. After spending almost a year training, it fought in the Allied counteroffensive during the Guadalcanal Campaign from December 1942, helping to end organized Japanese resistance on that island by early February 1943. The 25th spent a period garrisoning the island, then moved on to fight in the New Georgia Campaign in July. After the Japanese defeat in the latter it was sent to New Zealand later that year for rest and training, before moving to New Caledonia for further training. The division returned to combat in the January 1945 invasion of Luzon, reducing Japanese resistance on the island until late June, after which it was pulled out of the line for training. The division then served in the occupation of Japan after the surrender of the latter from September 1945.