The 4-320th FAR's beginnings can be traced back to America's entry into the World War I. As part of the nation's mobilization, 4-320th was constituted, organized and activated in August 1917 as Battery D, 320th Field Artillery (D/320th FA). As part of the original 82nd Division, D/320th FA played a key role at Lorraine, St. Mihiel, and the Meuse Argonne region in France. Following the Armistice, the 320th FA demobilized, only to be reconstituted in June 1921 as part of the United States Organized Reserves.