During the expansion of the United States Army in preparation for World War II, the unit was reorganized on 30 December 1940 as Battery A, 25th Field Artillery Battalion. On 19 December 1942 the unit was again reconstituted as Battery A, 604th Field Artillery Battalion and assigned to Camp Carson, Colorado as part of the newly formed 10th Infantry Division (Mountain). As part of the 10th Mountain Division, the unit departed the United States for the European Theater of Operations, arriving in Italy in January 1945. During World War II the unit earned campaign streamers for actions in the North Apennines, Po Valley, Rhineland, Ardennes-Alsace, and Central Europe. Following the conclusion of World War II in both Europe and the Pacific, Battery A, 604th Field Artillery Battalion was redesignated as Battery A, 25th Field Artillery Battalion and shortly thereafter inactivated.