3rd Battalion 6th Marines was activated on August 14, 1917, at Quantico, Virginia, as the 3rd Battalion, 6th Regiment. They were quickly deployed during October–November 1917 to France and assigned to the 4th Brigade, American Expeditionary Force. They participated in the following World War I offensive campaigns: Aisne-Marne, Saint-Mihiel and the Meuse-Argonne. They also participated in the following World War I defensive campaigns: Toulon-Troyon, Chateau-Thiery, Marabache, and Limey. Following the war they took part in the occupation of the Rhineland, December 1918-July 1919. They returned during July–August 1919 to Quantico, Virginia. The battalion was deactivated August 20, 1919