A gun mantlet is an armour plate or shield attached to an armoured fighting vehicle's gun, protecting the opening through which the weapon's barrel projects from the hull or turret armour and, in many cases, ensuring the vulnerable warhead of a loaded shell does not protrude past the vehicle's armour into the easily penetrated barrel. On many tanks during World War II, the gun mantlet covered both the main gun and any coaxial armament, and had the thickest armour on the vehicle.