The unit's history began on 17 September 1943 at Camp Peary, Virginia, where it was commissioned as the 133rd Naval Construction Battalion (NCB). After 7 months of training at Davisville, Gulfport and Port Hueneme the battalion's first overseas assignment was NAS Honolulu, Territory of Hawaii (May–October 1944). On 15 October 1944 word was received that the battalion was going to be attached to the 4th Marine Division. On 30 October the assignment came for Operation Detachment at Iwo Jima. D-day was planned for 19 February 1945. When 133 was attached to the 4th it was filling a billet that had been vacated when the 121st CB was released by the Marine Corps. The 121st CB had been transferred to the Marine Corps and re-designated as the 3rd Battalion of the 20th Marine Regiment. After the assault of Tinian the 20th Marines were inactivated. Then both the 1st battalion (4th Engineers) and 2nd battalion (4th Pioneers) were placed under Divisional control. Third battalion 3/20 or the 121st, was returned to the Navy creating the vacancy 133 was posted to. Before joining the 4th at Camp Maui, the 133rd was put through the Army's Pacific Jungle Combat Training Center (CTC) at Punaluu and Kahana Valleys on the north shore of Oahu, TH. It was a unit level training center to supplement Army Ranger and Army Combat training Schools. Camp Maui was located nearby at Haiku-Pauwela. The 133rd was the first unit to complete the course without a casualty according to their cruisebook.