 The Mortar Marines and Sailors, my name is Sergeant Keith, I'm an O-313. O-313 stands for Light Armor Reconnaissance Vehicle Crewman. We're mechanized infantry and as crewmen we have a driver, a gunner and a vehicle commander. My job as a gunner is tasked with employing the weapon system and destroying light armor threats, any type of aerial threats, any type of surface threats that may come in contact.