 In April 1942 , five months after the Japanese attack on Pearl Harbor , the unit was activated as part of the 2nd Marine Division . The headquarters was at Camp Elliot in San Diego , California , where it underwent intensive amphibious training . Before being reassigned to the 3rd Marine Division , the unit was assigned to Amphibious Corps , Pacific Fleet . The regiment was sent to Guadalcanal on July 1943 to relieve the 1st Marine Division . 2nd Battalion , 9th Marines participated in the Bougainville campaign of the Solomon Islands in the latter part of 1943 . On July 21 , 1944 , 2 / 9 participated in the invasion of Guam . The Japanese forces staged seven counterattacks , however the Marines prevailed despite the fact that they suffered over 50 % casualties . It was during this initial battle that one Marine , Captain Louis H. Wilson Jr . , ( who would in the future become a Commandant of the Marine Corps ) earned the Medal of Honor . 
