The Gun

The 1/92nd Field Artillery
Association - Vietnam

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Laying the Battery

By Tom Kanis

  Immediately upon occupying a position, all the Battery's howitzers would be "laid". This means that all their tubes would be pointed precisely in a known direction that would allow the FDC to send commands to fire them accurately. This helped to solve another of the Gunnery Problem' s aspects: the cannoneers cannot see the target.

  The Battery XO, AXO, Chief of Firing Battery ("Chief of Smoke") or the senior NCO present layed the battery. All Officers and NCOs were taught to lay the guns, which was a good thing, since the batteries were often split between locations. At one point in 1971 there were over 100 miles of roads between the left and right platoons of A Battery.

  Just as the best data available was used to shoot the guns, so was the best data available used to lay the battery. Survey data was best, followed by map and compass methods. If at all possible, survey control would be brought into the battery area by the Battalion Survey Section. Surveying from known points, they would bring both directional control and location control in on the same survey. The chief effect of this for the purposes of laying are concerned is that the Orienting Line was under survey control. The OL was a line from the Aiming Circle to a stake, and was usually pointed at grid north (AZ 6400). By subtracting the azimuth of fire from the azimuth of the OL (Memory Aid: "take the fire out of the old lady") the XO could properly set up the Aiming Circle to lay the battery.

  Reciprocal Laying was accomplished by using either surveyed or magnetic reference to North. This reference was used to place settings on an aiming instrument called an "aiming circle, M2" whited looked and operated a great deal like a surveyor's transit. Located in a place so it could be seen by the sights (The M12A7D panoramic telescopes or "pan-tel"'s) of the guns, the Aiming Circle was used to measure angles from a direction of fire to the pan-tel. The angle would be then set off on the scale of the panel and the gun moved either manually or with the traversing mechanism until the gunner saw the aiming circle in his pan-tel's eyepiece. The process was then done over again. The difference in angles would get rapidly smaller. Usually on the third try, there would be no difference between the angle read to the sight and the angle read back to the Aiming Circle by the gunner. The object of the exercise was to get the axis of the bore of each gun to be parallel with the direction ("Azimuth") of lay. When opposite interior angles (the numbers read out by the XO and gunner on their respective instruments) got down to no difference, the angles were equal and the lines were parallel. Thank you, Pythagoras and Plane Geometry!

  The commands to accomplish this were very ritualized. They had to be, seeing that we were required to accomplish laying very quickly in conditions ranging from broad daylight to tropical downpour at 0300 in a very dark morning. The person using the Aiming Circle, usually the XO or AXO, but sometimes the Chief of Firing Battery (a senior NCO also known as the Chief of Smoke) would command' "Battery adjust, Aiming Point this Instrument", each gunner would call back "Gun Number Three, Aiming Point identified", and so on until each gun had it's sights on the lens of the Aiming Circle. Deflections were read to the guns and each would set off the reading, and move the tube until the sight again pointed at the Aiming Circle's lens. When the measured difference in Gun and Aiming Circle reading reached zero, the XO would tell the gunner "Zero Mils! Number 3 is laid".

  Laying could also be accomplished in a pinch be using a distant aiming point on the horizon, such as a lone tree or hill. After occupying a position, each Gun Chief would make note of the deflection to a designated distant aiming point.

  Our beautiful 155mm Howitzers were from the time when the bad guys were always to the front and the good guys always to the rear. As consequence the sights and gun carriages were designed to swing left and right center about 400 mils. When it became necessary to shoot at a target further left or right or behind us, the guns would need to be jacked up on their speed jacks and swung around to center the azimuth of fire towards the new target. At that point, we needed to lay the battery again. Since much of the night lighting on the sights and Aiming Circles were antiquated and inadequate, we used a lot of flashlights and D-cell batteries to get the job done at night.

  Now that the guns were layed they could be fired by commands from FDC. But keep in mind that the gunners still cannot see the target. They needed some form of reference point to aim at, so, without moving the tube, the sights were swung around, usually to the rear or side of the gun, and a reference marker was set out. The principal reference point was a device called an "Infinity Reference Collimator".

  This could be a set of aiming stakes or an instrument called an "infinity reference collimator" which simulated a very distant aiming point. The reticle pattern in the pan-tel could look at the collimator or aiming stakes and make up for gun movement after each shot. Taking up the "piece displacement" meant that the guns were still pointed in the right direction. The collimator and aiming stakes were set out after the battery was laid. Once in place, a sliding scale on the pan-tel was set at a "referred deflection" in our case 2800 mils, so that despite irregularities in the areas around each howitzer, all sights would read the same numbers when looking at the stakes and collimators.