The Corps activated the 4th Raider Battalion in Southern California on 23 October 1942. Major Roosevelt commanded this new unit.
Jimmy Roosevelt had been Carlson’s XO in the 2nd Raiders and so brought with him all of Carlson’s gung ho philosophy as well the training and battle experience he had learned as part of Carlson’s Raiders.
The battalion was trained and organized at the newly formed Camp Pendleton. From October 23rd through February 8th, 1943 Roosevelt trained his men in Raider tactics and instilled in them the gung Ho philosophy.
On October 9th they set sail for the warzone.