3rd Assault Amphibian Battalion (3rd AABn) is one of two active duty assault amphibian battalions in the United States Marine Corps. The battalion's primary weapon system is the Amphibious Assault Vehicle or AAV. The AAV is a 26-ton armored vehicle that carries up to 18 combat-loaded Marines and is armed with the UGWS (UpGunned Weapons Station), which mounts a .50 cal (12.7 mm) M2HB machine gun and a Mk-19 40 mm grenade launcher. The AAV is the only armored vehicle in the U.S. inventory that is fully capable of operations both on land and in the ocean. The battalion is part of the 1st Marine Division and the I Marine Expeditionary Force. The unit is based in Camp Pendleton, California.