How to Put Steel on Target - Boresighting the M1A1

Eric Daniel

When the M1 series of tanks were first introduced in the 1980's they were hailed as the most revolutionary armored fighting vehicle to ever be produced. They had gyro stabilized cannons, thermal sights, laser rangefinders, jet turbine engines and a composite armor package. They were fast, they were well armored, and they were deadly accurate. This was especially driven home when D/4/8 Cavalry took their M1s to the 1987 Canadian Army Trophy (CAT) competition and destroyed the competition (the first place team, 1st Platoon D/4/8, out-shot the second place team, Germany's 2nd Platoon, 124 PzBtl. by 800 points (out of 21,800 points total.))

The reality is, though, the M1 tank didn't win that competition; the tankers of 1st Platoon did. As good at the M1's capabilities are, it is just a tool. The cannon doesn't load itself, the sights don't auto acquire targets, and the fire control system doesn't evaluate its own solutions. These are all crew duties and how well the crew does its thing will determine how well the tank does its thing.

While there are a whole myriad of things a crew has to do well in order to be successful, as a crew, the bottom line is, if you can't hit the target, you're not a tank; you're a 60 ton noise maker, and the very first thing that has to be done correctly in that long list of "to do's" before you put steel on target is boresight.

Boresighting the cannon and FCS involves aligning the cannon's point of aim with the tank's sights (the GPS (gunner's primary sight) located 2 feet above and 3 feet to the right of the cannon) the GAS (gunner's auxiliary sight) located just to the right of the cannon, and, in the case of the M1A2, the CITV (commander's independent thermal viewer) located opposite the GPS on the left side of the turret roof.) When properly aligned, the cannon and sights will all be looking at the same thing despite the face that they are all in different "planes" on the tank.

Step One: Inspect the Foundation

Prior to actually looking out the sight, the first thing you'll need to do is check your hardware, specifically the struts and trunions that hold the cannon in place. Even though the cannon assembly itself weighs several tons, it is not a rigid system. The cannon is held in place by a combination of load bearing arms as well as a hydraulic recoil mechanism. A cracked, broken or worn strut allows "slop" into the system, which would mean the cannon, when moved or fired, would not return to the same point of aim, which would obviously affect the quality of your boresight.

Step Two: Warm it Up

The turret and cannon are driven by hydraulics. Inputs from the gunner's power control handles (the GPCH or more commonly the "Cadillacs" referring to Cadillac Gage, the company that makes the handles) and the tank commander's power control handle (TCPCH or TC's "override") translate to valve commands to the turret's complex hydraulic system, providing the exact amount of pressure to move the cannon, in two dimensions, at the desired rate. This system is driven by a large hydraulic pump, which is, in turn, driven by an auxiliary gear system off of the tank's turbine engine. Since the hydraulic fluid expands as it warms up, before you start making the precise movements necessary for boresighting you're going to want to make sure the hydraulic fluid is at a uniform operating temperature. This is accomplished by cycling the oil through the system by spinning the turret several times in each direction, as well as elevating the gun between max and min elevation stops. In addition to warming up the oil, this also has the effect or working any air bubbles out of the lines, another potential source for "drift."

Step Three: Get your Drift to Zero

As previously mentioned, the turret is driven by a complex system of valves and hydraulic pressure. The electrical input system that drives the turret is extremely sensitive and minor signal flux in the cadillacs will cause the cannon to "drift." Drift is a regular occurrence and can easily be corrected (the GPS panel is equipped with both horizontal and vertical drift knobs to null it out.) If the drift, however, cannot be corrected, boresighting can't continue since the continuous motion will be incorporated into any fire control solutions you enter once you start shooting for real.

Step Four: TEST!!

Ok, your struts are good, your turret hydraulics are hot, and your drift is zero. Now it's time to run a diagnostic of the fire control system. The purpose of the self-test is to evaluate all the components of the FCS and to determine if there are any elements so far out of tolerance that achieving a valid fire control solution would be impossible. The self test is completely automatic; you just grab the cadillacs, hit the test button, and hold on -oh, important safety tip, before you do this, yell "Test!!" to let the folk outside know that the turret's going to be moving about. The self-test is pass/fail; either the system passes, or it doesn't. If the test fails the component that failed will be identified on the computer control panel (CCP), and you trouble shoot from there.

Step Five: Dump Everything

Once the self-test is complete, you're ready to begin the actual process of boresighting the system. Step one in this process is dump all your old data. Boresighting requires a lot of data to be manually entered by the gunner into the fire control computer in a methodical manner, but to initiate the boresighting procedures you need to begin with a blank computer "slate." This process is known as "dumping" or "zeroing" your data.

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Copyright 2012 by Eric Daniel