3rd Assault Amphibian Battalion (3rd AABn) is one of two active duty assault amphibian battalions in the United States Marine Corps

United States Marine Corps

The United States Marine Corps is a branch of the United States Armed Forces responsible for providing power projection from the sea, using the mobility of the United States Navy to deliver combined-arms task forces rapidly. It is one of seven uniformed services of the United States...

. The battalion's primary weapon system is the Amphibious Assault Vehicle

Amphibious Assault Vehicle

The Assault Amphibious Vehicle —official designation AAV-7A1 is a fully tracked amphibious landing vehicle manufactured by U.S. Combat Systems .The AAV-7A1 is the current amphibious troop transport of the United States Marine Corps...

 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

Mk 19 grenade launcher

The Mk 19 Grenade Launcher is a 40 mm belt-fed automatic grenade launcher or grenade machine gun that entered U.S. military service during the Cold War, first seeing action during the Vietnam War and remaining in service today.-Overview:...

. The AAV is the only armored vehicle in the U.S.