Abstract: A gun sighting system in which a daylight (visual) sight and a thermal imaging (TI) night sight are mounted on the gun breech. The TI field of view is superimposed on the visual field of view, necessitating accurate alignment between their lines of sight and the gun muzzle boresight. Adjustment of the visual sight causes separation of the visual and TI displayed images which is indeterminate in the absence of distinct target features. In accordance with the invention a visual reference mark is injected on to the field of view, which reference mark is locked to the target scene. Separation of the visual and TI scenes causes corresponding separation of the reference mark and TI sight line marker thus permitting adjustment of the TI field of view to remove this separation and align the visual and TI scenes.