4th Tank Battalion (4th Tanks) is an armored battalion of the United States Marine Corps reserve. Their primary weapon system is the M1A1 Abrams main battle tank and they are part of the 4th Marine Division and Marine Forces Reserve. The unit headquarters is at the Navy and Marine Corps Reserve Center San Diego, California but other units in the battalion are located throughout the United States. With six lettered companies, 4th Tank Battalion is the largest Marine tank battalion.