Activated on Armistice Day (November 11) in 1943, the 5th Marine Division first began its official operations on the first day of December at Camp Pendleton in California. Eventually, units from the Division began to deploy to Camp Tarawa, a facility constructed by Marines from the 2nd Division returning from the Battle of Tarawa. One of the 5th Marine’s four regiments, the 28th, had somehow talked the Navy into allowing them to bring a lion cub it had purchased for $25 from the Griffith Park Zoo in Los Angeles. But when it came time for the 5th to ship out for its first combat mission, the Navy ordered that the mascot, named Roscoe, be left behind.
That mission was the amphibious assault on Iwo Jima, and despite a massive aerial bombardment campaign—the 7th Air Force dropped close to six thousand tons of bombs on the tiny island over the course of 70 days preceding the landings—the Japanese were thoroughly entrenched and prepared to fight to the last man. Of the 17,607 officers and enlisted personnel organic to the Division when the invasion began, 2482—14 percent—were killed in action, and the total casualty rate was 42 percent. The Division was awarded a Presidential Unit Citation for its role in the battle as part of the 5th Amphibious Corps, which also comprised the 3rd and 4th Marine Divisions.
The Division was inactivated in 1946, but in 1966 the expansion of the American military presence in South Vietnam led to the activation of various subordinate units that had been attached to the Division and then, on 1 March 1966, the activation of the Division Headquarters. While the Division as whole was never deployed to Vietnam, several of its sub-units (regiments and battalions) served during the war, garnering three Presidential Unit Citations. The Division was inactivated on 26 November 1969.