3rd Battalion 3rd Marines was activated on 1 June 1942 at New River, North Carolina as the 5th Training Battalion, Division Special Troops, 1st Marine Division, Fleet Marine Force. On 16 June, they were redesignated as the 3rd Battalion, 3rd Marines, Fleet Marine Force. From August to September 1942, 3rd Battalion deployed with the rest of the 3rd Marine Regiment to Tutuila, American Samoa and was reassigned to the 2nd Marine Brigade. In 1943, they were reassigned to the Fleet Marine Force. In May 1943, they redeployed to Auckland, New Zealand and in June, were reassigned to the 3rd Marine Division. From July to August 1943, they redeployed to the island of Guadalcanal to begin training in preparation for the invasion of Bougainville in November.