 2nd Battalion , 9th Marines ( 2 / 9 ) was an infantry battalion of the United States Marine Corps . Formed during World War I , the unit played an instrumental role in the defeat of the Japanese forces in the Battles of Guam and Iwo Jima during the World War II . The battalion distinguished itself in the defense of Khe Sanh during the Vietnam War , and later participated in an ill <unk> invasion of Koh Tang Island in Southeast Asia , with the intention of rescuing the crew of the SS Mayaguez . During Operation Desert Storm , the battalion served as the lead battalion for the III Marine Expeditionary Force ( III <unk> ) . 
