Self-propelled guns are mounted on a motorized wheeled or tracked chassis. As such the gun can be maneuvered under its own power as opposed to a towed gun that relies upon a vehicle or other means to be moved on the battlefield. Self-propelled guns are combat support weapons; they are employed by combat support units fighting in support of, or attached to, the main combat units: infantry and armour. Self-propelled guns are best at providing indirect fire but can give direct fire when needed. It may be armoured, in which case it is considered an armoured fighting vehicle (AFV). Typically, self-propelled guns are more lightly armoured and may not have turrets and their purpose is distinct from that of tanks.