Abstract: A fire control system for aiming a cantilevered adjustably mounted gun indes a flat muzzle mirror fixed to the muzzle of the gun. A light source, disposed within a gunner's periscope, directs a beam of light onto a movable mirror, in the periscope, which reflects the beam normal to the muzzle mirror only in the absence of gun to periscope positioning errors for all positions of the gun. The reflected beam from the muzzle mirror impinges on a charge coupled detector matrix array; and, depending upon the portion of the array impinged upon, provides compensatory azimuth and elevational error signals which are algebraically added to azimuth and elevational range signals produced by a ballistic computer in response to a range finder sighted on a target. The compensated azimuth and elevational signals are employed to position a movable reticle correctly in the periscope to enable the gunner to aim the gun accurately, whereby to increase the first round hit probability.