On May 1, 1942, the 1st Training Battalion was activated at Marine Corps Air Station New River, North Carolina. A month and a half later, on June 17, the unit was redesignated as the 1st Battalion, 3rd Marine Regiment. The battalion received its first combat experience in November 1943 against the Japanese in the Battle of Bougainville. The battalion fought with distinction for nearly two months against stiff resistance in difficult terrain before being sent to Guadalcanal to prepare for the next stage of the Pacific Theatre.