Artillery is a class of large military weapons built to fire munitions far beyond the range of infantry's small arms. In contemporary usage, it usually refers to shell-firing guns, howitzers, mortars, rockets, and guided missiles. Modern equipment can either be towed or self-propelled (SP). A towed gun fires from the ground and any inherent protection is limited to a gun shield. In Self Propelled equipment, the gun is an integral part of the vehicle that carries it.