When the 19th CB was assigned to the Marine Corps 11/05/42 it lost one company and 1/4 of Hq Co.19th Naval Construction Battalion Historical Information, Seabee Museum website Those men were assigned to the Fleet Marine Force Replacement Group, New River, NC (19th replacement group) which would form the core of the 121st CB when it was formed 05/03/43.121st Naval Construction Battalion Historical Information, Seabee Museum website On 7 July 43 the Battalion was redesignated as the Third Battalion Twentieth Marines. The Battalion was shore party for the 23rd Combat team on beaches blue 1 and 2 on Saipan.
