US Patent 7124676 Muzzle reference system

In systems embodying the invention, a battery powered collimated light source is located at the muzzle end of a cannon and is beamed back over the length “L” of the cannon gun tube to the collecting aperture of an optical transceiver located near the breech end (or trunnion) of the cannon. The turn-on and turn-off of the collimated light source is under the control of the gunner of the tank or the tank's fire control computer system to ensure that the battery power/energy is used only when deemed necessary by the user so that battery power is conserved.