The battalion was first formed on May 12, 1943, at Marine Corps Base Camp Pendleton, California. It was composed, with the exception of 2 officers, entirely of reservists. It was the first unit to capture Japanese mandated territory in the Pacific. It participated in the Battle of Kwajalein, Battle of Saipan, Battle of Tinian, and the Battle of Iwo Jima. For Iwo Jima the unit was augmented with four M4-3A Shermans that had the main armament swapped for a CB-H1-H2 flamethrower. As the troops became aware of the weapon they had they would hold up their assault and wait for the tankers with their CB-H2s. Ground commanders felt it was the single best weapons system at their disposal. On Iwo the tank battalions from all three Divisions were formed into a Regimental command lead by Lt. Colonel William R. Collins of the 5th. It was the largest USMC armour command of the war.