20th Marines was formed on June 15, 1943, During the war the Regiment involved in the battle of
Roi Namur,
Battle of Saipan and
Battle of Tinian. On Saipan, the 4th Marine Division assigned 2/20 and 3/20 (4th Pioneers and 121st CB) as the shore party The regiment was inactivated on August 31, 1944 with the 4th Engineer and 4th Pioneer Battalions reassigned to the Division itself. While the 121st NCB remained at Tinian to work on the airfield, the 4th moved on preparing for Iwo Jima. 133 NCB was posted to the slot vacated by the 121st. With the 20th Regiment gone the 133rd was assigned to the 23rd Marines as their shore party and the 4th Pioneers were assigned to the 25th Marines as theirs. The 4th Engineers were then under divisional control. A note concerning the 121st. That Battalion had Marine Officers assigned to it. When the 19th CB was assigned to the Marine Corps 11/05/42 it lost one company and 1/4 of Hq Co. 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. 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. '''Regiment's Commanders''' • Lieutenant Colonel Nelson K. Brown (15 June 1943 - 22 August 1943) • Colonel Lucian W. Burnham (23 August 1943 - 9 April 1944) • Lieutenant Colonel Nelson K. Brown (10 April 1944 - 31 August 1944) ==Unit awards==