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Gunnery Fire Control - Part 1.
The Sheridan I had used two different sights. One for day and one for night engagements, I THINK. I spent very little time in Sheridan gunner seats. I know that the day sight had a stadia reticle so that the gunner saw lines that looked a funnel, open end up and with cross bars for range. (This is for conventional rounds. I don't remember what the missile sight looked like.) The TC was equipped with standard binoculars that had a reticle that was basically the same. The TC would make an estimate of the range to the target, lay the turret as close as possible to the target bearing with the override, and issue the fire command. If the vehicle was moving it would start with "Driver stop!" (We always fired from a short halt if we were moving.) If the gun wasn't loaded, or even if it was, "Gunner, HEAT, Tank, range 800." If you wanted to fire a different type of ammunition for the second shot you would add something like, "Loader, load canister." When the gun was loaded the loader would say, "Up!" If the gunner was able to see the target he would say, "Identified!" I think I was supposed to say, "Fire" at that point but somehow I got into the habit of saying, "Send it." (I actually worried about that a few times. What if I got a new gunner?) Just before the gunner fired he would say, "On the way." If the round hit the target I would say, "Target, cease fire." If not I would give an estimated correction, etc. etc.
The way that the stadia reticle worked was based on the width of the target and could get pretty confusing. The gunner had to 'choke' the target in the funnel, in other words, elevate or depress the gun until the target just barely touched the lines on both sides of the funnel. Then the calculations began. If it was a direct side shot at a Russian tank the gun elevation was correct. If it was a front shot, the actual range was half of what the nearest crossbar indicated. If it was a 3/4 shot the range was 3/4 of the indicated range. If it was a vehicle smaller than a tank, and a frontal shot the range was actually 11/17ths or something like that. The gunner would usually start off using the TC's estimated range rather than do the math, which put a lot of pressure on the TC. The later models of the Sheridan's, and the M60A2, had laser rangefinders that returned at least three ranges for each time it was triggered. It was up to the TC to guess which one was the best. If they were all the same, it was a no-brainer, but they usually differed by several hundred meters, especially in Germany. There were also spaces in the range crossbars at 5 mil intervals for use when firing at moving targets. Using these usually involved pure guesswork.
I'm a lot surer of the fire control system in the M60A1s and A3s. The fire commands were the same but the TC had an optical coincidence range finder. I spent a lot of time practicing with this because, although it sounded simple, a lot of TCs appeared to have trouble with it. The TC started off with the override to get a fairly fine 'lay' on the target. There was a simple reticle with aim off lines for moving targets and a simple vertical line for azimuth. The principle was that each end housing, mounted on opposite sides of the turret at its widest point, projected an image onto a system of mirrors. One image was slightly dimmer than the other and was called the 'ghost'. The TC had a knob that he rotated to change the orientation of one of the mirrors until the two images coincided as closely as possible. At that point the range to the target could be read off of a scale above the knob. The range finder was connected to both the gun, so that it elevated and depressed with it, and to the ballistic computer, which was a box full of cams with a separate cam for each major type of ammunition. At this point, if all of the linkages were working correctly, the gunner's sights should be just about to the point where he could fire. (The gunner had a 'T' handle to select the proper cam for the type of ammunition currently in the breech. Some gunners were a lot better about remembering this part of the process than others.)
The gunner had three sights. Two were periscopic (day and night) that had the lenses mounted in an armored guard on the top of the turret. The third was telescopic, mounted coaxially with the gun and which used the infamous stadia reticle, considerably stretched vertically because of the max sighting range of 4200 meters as opposed to the Sheridan, which might have gone out to 2000 meters. I think that there were two or maybe three different reticles selectable to compensate for the different types of ammunition. (Maybe I donít remember it as well as I thought.) The periscopic sights had the same type of reticle that the rangefinder had. The concept was that, if the TC had used the range finder correctly, and the linkages were all in good shape, and the cams in the ballistic computer were not worn, and the right one was selected, and the target was not moving, and the wind was not blowing, all the gunner had to do was lay his cross hairs on his favorite part of the target and pull the trigger. Unfortunately, this particular set of circumstances seldom occurred.
In Sheridans and M60s the gunner had no foot controls. He had a small partial steering wheel like device used for hydraulically traversing and elevating the gun. This was called a Ďcadillací control because it was made by Cadillac-Gage. It was probably the basis for a lot of the computer game controls that are now in use. The grips had finger indentations on the front. There was a trigger under the index finger on each side and a longer lever that controlled the turretís magnetic brakes under the other three fingers, again on both sides. (If you wanted to stop a high-speed turret traverse in a hurry, and didnít mind having your turret mechanic take you off his Christmas card list, just let go of the mag brake levers when the turret is moving very fast and then let the wheel straighten itself out. It was spring loaded to the neutral position.) The gunner also had an emergency firing device, which was just a hand-operated magneto that would produce enough electricity to fire a round if the tank was disabled. There were also manual traversing and elevating controls in case of hydraulic system failure or an electrical failure. The manual elevation handle had another trigger just in case. They were tedious to use on flat ground and became quite a challenge if the tank was tilted to any large degree because of the asymmetrical weight distribution of the turret.
One of my other bad habits was that I always bore-sighted and zeroed my own gun. American doctrine was that this should be a normal crew function but most of the time I didnít have a crew, and when I did, I usually didnít know what their capabilities were. Bore sighting and zeroing are fun, especially my way. The first step is to stretch white threads between the Ďwitnessí marks (four punch marks in the forward edge of the gun barrel that were 90 degrees apart) at the muzzle of the barrel. Then you pulled out the firing pin and, while watching through the firing pin hole with a pair of binoculars, you laid the center of the cross hairs on the center of the zeroing panel target, which was a surveyed 1200 meters away. Next, you adjusted the gunnerís telescopic sight so that itís 0 meter line cross hairs were laid on exactly the same spot. I always did the telescope second in case my threads blew away or shifted because, after the telescope was done, I could use it instead of the threads. Next was the range finder which Iím pretty sure was done with the ballistic computer turned off. There were two adjustments needed to make sure that the sights lined up exactly with the threads and the telescope. I think I had to have the range set to 0 meters. After that I did the gunnerís periscopes using a piece of cardboard with a pinhole in it to do the night sight. Once all of the sights are pointing as close as possible to the exact same spot at 1200 meters any differences caused by the difference in distance between the lens of that sight and the axis of the bore were considered to be insignificant.
The next phase was zeroing. Four rounds, usually HEAT, at a 1200 meter panel. There was only one occasion where I was not able to zero in four rounds, and on that occasion I had let my gunner do part of the work. I started all over again with bore sighting, without the gunner, and zeroed in four rounds. The concept is that you fire three rounds at the panel, being sure that your point of aim is as close as possible to the same each time, then lay the gun on the same point of aim again and move the sights to the center of the three round group. Then you lay the gun on the center of the bullís-eye again and fire, and the round should hit within the bullís-eye. If it doesnít then you were not zeroed.
I never zeroed with turret power on. Everything was done manually, in a certain sequence, and firing was done with the emergency firing device. I didnít want anyone touching anything that might move the turret when the gun was fired so I didnít even use the trigger button on the manual elevation handle. To lay the gun on the target, and I only used the telescopic sights for this because they had less linkage attached, I would depress the gun, traverse left past the target, traverse right back to the target, then elevate the gun until the 1200 meter line and the vertical line were dead center in the bullís-eye. If my point of aim ended up being even a little bit off, I would do it again until it was exactly on. This often took me quite a while, and I had to refuse to move on once because I wasnít satisfied, but it was very important, and I believed that it was well worth the effort. Once again, this method would be of questionable value in a real situation.
Many years ago I read that the Israelis, who are probably on average the best tankers in the world, had a Master Gunner for each unit that bore sighted and zeroed all of the guns in his unit. I would have a lot of difficulty accepting this, but many Israeli tankers are reservists and it might be difficult for them to maintain the required skill level.
Both Sheridans and M60 were supposed to have fully stabilized turrets. (Azimuth and elevation) I hardly ever used turret stabilization because there wasnít much requirement for it in peacetime when safety was considered more important than firing on the move. I think I turned on the turret stabilization in my Sheridan once and immediately scared the Hell out of everyone, including myself. I think that we were required to fire one moving, stabilized engagement during my second gunnery qualification in Germany. Other than those two occasions the ĎTurret Stabí toggle switch was probably the least used control in any of my tanks.
My thanks yet again to Rory.
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