What is muzzle reference system in tanks?

Answer 1

Being deeply involved in the UK MoD's original developments of tank-bourne Muzzle Reference Systems (or....MRS, as it is commonly referred to), I can answer this with some experience.

As tank barrels became, through evolution and the need to shoot further and more accurately, basically longer and longer in length, there became inherent difficulties in maintaining accuracy of these long barrels. Believe it or not, how ever sturdy tank barrels appear, they bend, frequently in use. Tank barrels bend especially as they gain heat from repeated firing and/or through differential cooling due to, say, winds, snow, rain, etc. [More normally a combination of those former factors]. Accepted that the last metre or so of the pointing direction of the end (or muzzle) of a tank barrel determines the direction of the projectile fired, it is easy to see that the aiming device of a tank, ie the tank sights (or more modernly the tank's fire control system) must keep as accurate as possible harmonisation [or co-alignment] with the pointing direction of the muzzle end of the barrel as it goes through these deformations during firing.

In order to maintain accuracy of fire and compensate for this thermally-induced inaccuracy in modern tank barrels, a system was developed around ,simply put, a light projector (mounted at the tank's turret) which bounced light off a mirror at the muzzle end of the barrel and back into the gunner's sight. In use, the system would be initially accurately aligned with the gun muzzle (by 'boresighting'....I'll keep that a separate subject) and, as the thermal deformations in the barrel occurred during use, the deflections at the muzzle could be checked by the movements in the reflected light spot back into the gunner's sights and the gunner could alter his sight co-alignment with the barrel end by adjustment of 'x' & 'y' of his zero aiming point. Therefore the system was termed a 'reference' system, in that it takes account of inaccuracies induced after first accurate alignment, or reference, of the sights to the gun muzzle.

Formally, I said 'simply put', because the technical difficulties in developing and producing accurate and stable devices to allow such a system to succeed in arduous tank battle conditions are massive. I believe I cannot, to this day, divulge the technical details of what the systems comprise, save to say that they are and have been developments of complex opto-mechanical, precision technologies working in some of the most violent conditions and environments man can produce for such equipment.

I was involved in the initial developments of the system, up to its acceptance into service, as a 'manually adjusted' system, ie the tank gunner had to check his Muzzle Reference System and manually adjust his zero on the tank's sights. However, as I moved on from by involvements, fully-Automatic Muzzle Reference Systems were being discussed and that is where the technology has progressed to today; fully automatic compensation and constant accurate alignment between the firing controls of the tank gunner and the aiming direction of that critical last metre or so of the end of the modern-day tank's long barrel.