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The Chieftain's Hatch: Fire on the Move

This is the last in the series of articles stemming from the US Army’s testing of Centurions II and III in late 1949/early 1950. We’ve already seen that they concluded that Centurion was a fairly competent vehicle, albeit that it was expected that the next generation of American tank would be no worse than equal in various characteristics, but they were particularly curious about the stabilization system as up until that point, nothing had been put into service on a tank which was claimed to provide a true fire-on-the-move capability. The gyrostabilised guns on American tanks in WWII, being single-axis only, could not make such a claim. As we go through the observations below, I suspect that even in the M4 the Americans had already started noticing such things, but it is still interesting to see how they are officially reporting them below. Anyway, I’ll let you read the observations, and will come back to you afterwards.


1. PURPOSE. To determine and depict operating conditions peculiar to firing on the move with the Centurion II in order to effect a better understanding of the difficulties experienced in fighting a moving tank.


a. The conditions affecting the crew and the manner of performance of individual crew members were carefully observed during all stabilized firing and nonfiring runs carried outwith theCenturions. Observations were analyzed and, in addition, the reactions of various users were determined and evaluated.

b. The effectiveness of the Centurion fighting compartment and its various turret components is fully covered in Army Field Forces Board No. 2 Preliminary Report of Project, No. 1365, Test of Stabilization, Fire Control, and Main Armament of British Tank, Centurion III, 2 Dec 48. As a result, reference is made in the subsequent discussion to these specific facilities only when required for better understanding of the action involved or when a particular facility has a direct effect on the manner of performance of a crewman.

3. RESULTS. Crew efficiency was noticeably lessened when firing on the move with the Centurion II, and this disadvantage was only partially offset by increased training and vigilance. Moreover, under the conditions encountered in a moving tank, the duties performed by the tank commander and gunner were mentally and, to some extent, .physically fatiguing. Those carried out by the loader were especially tiring and, in some, instances, hazardous. It should be noted, with respect to operating conditions, that the Centurion provided a relatively stable firing platform, and it was observed that the crew of the British tank could function with reasonable effectiveness at combinations of speed and terrain which completely nullified the efforts of crewmen in the lighter, shorter M4A3 and M24 tanks. Nevertheless, even in the Centurion, the rate and accuracy of fire suffered because the crew itself was hampered by the random motions of the tank. As a result, it would appear, in view of thecrew's instability and resultant inadequacy, that there is a practical limit to stabilizing accuracy in so far as tank armament is concerned. However, it should be appreciated that the adverse operating conditions, which are to be expected when firing on the move, can be tempered considerably by providing suitable crew facilities. This evidenced in the subsequent description presented from the standpoint of each crew member, of conditions experienced when firing on the move with the Centurion II.

 a. Gunner. In gunning on nonstop, stabilized runs, the tank gunner was decidedly handicapped by the random motions of the tank and his own resultant instability. Lateral support, especially for the head, was lacking. Moreover, a conventional seat with backrest and footrest was inadequate.

 (1) As a consequence, the operator was largely dependent on the support afforded by the power elevatingand traversing controllers. Their continued use, in turn, was fatiguing because no arm rests were provided and because it was necessary to manipulate the controllersfor extended periods against the action of centering springs. These conditions were aggravated by the relative back-and-forth motion of the periscopic sight. Pitching or rolling occasioned by major obstacles or a series ofcomparatively low but abrupt bumps negotiated at high speeds, as a result, usually precluded viewing the reticle despite the gunner’s efforts to support himself and to conform to the travel of the eyepiece. In effect, the benefits accruing from stabilizing the gun and turretin elevation and azimuth respectively were frequently offset by the inadequacy of the gunner.

 (2) Furthermore,the gunner, of necessity, relied on indirect vision, aperiscopic sight with a unitpower windowand an eyepiece with a magnifiedfield.The latter was, of course, impractical for visual ranging, and the small field of the unit-power window so limited perspective, especially when moving, as to makeperception of distance difficult. Moreover, it was virtually impossible for the gunner to visualize range as a function ofthe displacement of the firing tank or to judge the speed of a movingtarget. It was also hard for the gunner to remain cognizant of the relationship of the turret to the hull in azimuth.

 b. Commander. Similarly, the tank commander was hampered by vehicular pitching and rolling when operating on the move. As a result, he usually had to use one hand to steady himself, and he had to be careful to avoid being fouled by the vertical movement of the main armament deflector guard.

 (1) Experienceindicated that it was advisable for the commander to stay within the cupola duringa firing run. This practice, besides being the safest, provided protection from muzzle blast and a greater measure of stability, and placed thecommander close to key controls. This position also enabled him to view activities within the fighting compartment and to exercise close supervision. Operating within the cupola, on the other hand, was not without disadvantages. It was, for instance, relatively easy to get get buffeted about the head, particularly from the clutter below the cupola ring. However, some protection, as well as support, was gained from the browpads above each vision device.

 (2) Operating from within the cupola also made the commander completelydependent on optical means for viewing. Unlike the gunner, however, the latter [Sic. Presumably intended former] could use theunit-power windows around the circumference of the cupola to note the distance travelled and could base subsequent range changes on that displacement. Nevertheless, visual determination of range on the move was more difficult, and probably less accurate then estimating distance from a stationary tank. It was also necessaryfor the commander, who lacked a stabilized viewing device, to rely solely on unit powervision when moving. It proved impossible to control by hand, in opposition to vehicularpitching, amagnified field regardless of the degree ofdampening embodied in the mounting. Hand-held binoculars, of course, were useless under such conditions. This, naturally, did not affect visual ranging, but it did handicap observation of fire and detailed scanning from a moving tank

 (3) In addition, obscuration was alleviated only in special situations by the movement of the firing tank. In fact, visibility was worse, if anything, when the course followed by the tank was dusty or contained pools of standing water. In any event, sensing of the tracer trace of shot-type ammunition was impossible in most instances, although it was possible on occasion to spot an actual strike. High explosive bursts, on the other hand, could be seen more readily then shot strikes, but sensings were less exact than when made at a standstill.

 (4) It should also be noted thatavision cupola, which can be rotated independently of the turret, was of doubtful value when used on the move. In the first place, theeffort needed to slew the cupola by hand was excessive in view of the commander’s instability. Secondly, the speed of rotation using a handwheel was too slow and compared unfavorably with the quickness with which the operator’s head and body could be twisted to view to the flanks and rear. Orientation, using a rotatable cupolaon the move, was also difficult, especially if the tank was moving in one direction and the cupola and turret were facing in a second and third.

 c. loader. Although the elevation of the stabilized gun remains relatively fixed during a firing run, the effect is quite the opposite in so far as the loader is concerned. In fact, it appears to him that the armament, primary and coaxial, oscillates within the limits of elevation and depression. This effect is caused by the relative motion of the nonstabilized floor of the fighting compartment, which pitches with the tank, and the stabilized gun mounting. To add to the loader’s discomfort, his platformrolls with the tank and, unless fastened to the turret, yaws with the hull. If fastened to the turret it, of course, shifts in azimuth as the turret is traversed.

 (1) As a consequence, loading, when under way over cross-country course, was difficult and fatiguing. However, it was not as hazardous as commonly expected, despite the random platform motions and the sometimes violent swath cleared by the guns and mounting when the tank pitches. Nevertheless, a potential danger existed as it was always possible for an unexpected bump to catch the loader unaware and off balance. This was particularly likely if the loader had a cumbersome round of ammunition in hand, and it was doubly dangerous under such circumstances because percussion primers are susceptible to spuriousdischarge and brass ammunition cases are easily distorted.

 (2) In such instances, the loader's security depended largely on his footwork and, to a lesser extent, on the support gained by leaning against the side of the fighting compartment or on the quickness with which he regained his seat. It should be appreciated, therefore, that not only the loader's efficiency but also his, as well as the crew's safety rests on the provision of adequate working conditions. In this connection, there is no substitute for working room, especially alongside and underneath the breech mechanism. Even the absence of a rotating floor in the Centurion was not objectionable inasmuch as there was ample foot room. On the other hand headspace, sufficient to stand fully erect, was less critical than lateral space, provided there were no overhead projections and, further, that the loader did not actually have to crouch to work.

 (3) Ascould be expected, it was impracticable to withdraw ammunition from bins underneath the subfloor while moving. Furthermore, access to reserve bins outsideof the fighting compartment was contingent on turret position and clearance provided. At best, replenishment of ready rounds from such bins is a hit or miss proposition unless carried out with the turret deliberately locked in a favorable position, As a result, the ammunition available on a nonstop firing run was essentially limited to that stowed within the turret basket.

 (4) The speed of loading, of course, depended on the ease with which each of these ready rounds could be withdrawn and positioned for ramming. The latter step naturally involved inserting the nose of the projectile into the relatively small opening in the breech which, as previous1y mentioned, moved up and down with respect to the loader’s platform. As a result, loading would have been very troublesome if the loader had been unable to see the breech opening, if he had had to lift the round over the sideof the breech ring or deflector guard, or if he had had to reference the roundother than with respect to the breech. In fact, if the base of a round, with its nose entering the chamber, could have fouled any part of the interior of the turret between the limits of elevation and depression, there would have been· danger of injuring the loader and of bending the shell case under the dynamic conditions existing in a moving tank. The possibility of damaging the ammunition would be especially acute under such circumstances if discarding sabot ammunition were involved, because with this type of round, it is relatively easy to separate the subprojectile from the carrier

 (5) Loading, incidentally, for a right-handed person is greatly facilitated, especially if the ammunition is bulky, if he works from the left side of the gun.

 (6) After loading, it was imperative that there be a slight delay prior to firing in order to allow the loader to clear the recoiling parts. Otherwise, it is always possible for a sudden lurch to throw the loader into the path of recoil. It was equally necessary to provide for the control and collection of empty brass. Spent cases, cluttering up the turret floor, would hinder the loader and, in addition, might jam the turret.

 d. Driver. Driving conditions on nonstop firing runs were not unusual except that visibility was frequently reduced by muzzle blast, especially when dust or pools of standing water were encountered. In fact, when shots were closely spaced, the driver was blinded for as long as a third of a minute at a time.


And thus ends that series of observations.


Again, it must be observed that some of these things appear blindingly obvious. However, we have two advantages. The first is that, well, we’re familiar with these problems. We’ve grown up with fully stabilized systems and the problems of operating in a tank so equipped. The other is the converse: We did –not- grow up in an environment of unstabilised tanks, and so did not have to ‘unlearn’ much of what we had learned about what a tank is capable of and how to operate within one. Although something of an exaggeration, it can be more or less surmised that prior to the advent of stabilization, tanking could be combined into two different periods. The moving period, in which case the driver and a turret crewman, likely the loader, would be responsible for driving, the TC for observation or platoon/company leadership duties, and the gunner basically just held on and looked at what he could. And there was the fighting period, in which case the driver didn’t do much, the gunner and loader serviced targets with great efficiency, and the TC ‘fought’ the tank, or if it was an officer, left the loader and gunner to their own devices while controlling the platoon/company. With the advent of stabilization, though, everything could happen at the same time. I will speak from experience that I’ve never had information overload to the same extent as my first ‘platoon-in-contact’, in which case I’m trying to control a platoon, including keeping an eye on where they are with respect to me, keep track of where the hell I am on the map, find, prioritize and engage the enemy, figure out where –they- are on the map, fight the tank itself, co-ordinate with other elements, and all while trying to do this inside a moving vehicle. It’s bad enough when stationary, and if you’re in a vehicle which wasn’t designed for it… well, you can imagine the problems.

 As I go back over the report, a few things do stand out.

 Gunner stability. One of the biggest problems with shooting on the move which seems often overlooked is that there are two components to the fire control system. Modern, independently stabilized two-axis sights, combined with fire control computers that take everything imaginable into account, and with a computerized interlock that can delay firing until the gun and sight are both aiming well in the right place at the right time, can basically nullify the effects of the pitching tank. But, garbage in, garbage out. This multi-million dollar computer system is only as good as the inputs being given through the controls, and here’s this bit that people miss. If the tank is being thrown about due to the pitching caused by the uneven terrain, the poor gunner is similarly being thrown about and is holding on for dear life to prevent himself from being slammed into one of the many components inside the tank. And, as mentioned, in these early vehicles, even the sight isn’t stationary, as it is connected physically to the gun which is moving independently, and the sight is something you don’t want to impact if you want to attract a date when you go back to civilian life. You also can’t be too far from it, as magnified optics have a ‘sweet spot’ in which you have to place your eye in order to see anything at all.

 Note the line “the operator was largely dependent on the support afforded by the power elevatingand traversing controllers”, and think about what this means to the concept of gunning on the move. Imagine, for a second, you’re in the passenger seat of a Land Rover being driven enthusiastically offroad. Sure, you’re sitting down, and you probably have a seatbelt on, but the manufacturer has thoughtfully provided a Jesus Bar for your use. (I’m sure it has some official name like “Passenger’s Safety Handlebar”, but I’ve always known it as the Jesus Bar). Now imagine the forces being applied to this bar by your hand as you are using it to prevent yourself from being thrown around. These are the sorts of forces which the gunner of a tank will be applying to what his hands are holding, for the same purpose: To stop him from being thrown around. The problem is that he’s holding the gun controls, so he now has to apply not only the forces necessary for self-preservation, but also the forces necessary to aim at the target. How can he conduct a steady lay by having to balance these entirely competing, and rapidly changing requirements? Basically, he can’t. So not only do you have to stabilize the fire control system, you have to stabilize the crew. The best way to do that is the suspension. For that, you’re looking at a variety of factors varying from suspension type through, as the report mentions, overall length of the vehicle. It is to be noted that the oft-derided over-complex German interleaved suspension did have the reputation of providing a notable smoother ride, so instead of having a stabilized gun, such as the American tanks had, the Germans had an entirely stabilized crew, which benefitted everyone’s duties. And neither could truly fire on the move. Later on, they figured out other ways of stabilizing the gunner. If you look into an Abrams today, you’ll see the gunner is pinned in place between the backrest and a chestrest, and the British tank’s gunners controls take it to the ultimate by having the handles bolted into place, allowing the gunner to use them for final stability, with the turret being controlled by a thumb control stick similar to that found on a console game controller. I can’t say I’m convinced by the level of fidelity provided by it, but I didn’t try it for enough time to get used to it. Either way, however, much effort has been taken to address the fire-on-the-move difficulty, far beyond simply coming up with a better gun stabilization system.

 With respect to the loader, a few other observations were made, which are relevant today. The first, of course, is the position of the ammunition reloads. Note that Centurion II and III have only a four-round ready rack. Even if you drive with a round in the tube, given you want to have a couple of different rounds immediately handy, that means that the Centurion II or III loader will only be able to get two or three shots off before being forced to start digging around in the rest of the vehicle for more rounds of the appropriate type. And with the vehicle bouncing around, even the six rounds under the gun may be a little disconcerting to reach (The video shown in Part II, from the speed of loading, had, I guess, a round in the tube, a round in the loader’s hand, and the four ready-rounds filled when they started the filming run). As the tank is fighting on the move, it is obvious that having more rounds inside the turret, and better yet, inside the turret and away from the gun, is more likely to be of use to the loader. Later marks of Centurion fixed this somewhat by expanding the turret basket and having rounds sitting on the turret’s floor.

 The other question, that of loading the gun on the move, to my surprise remains rather unaddressed in some tanks such as Abrams. If you watch Leopard 2 or Challenger 2 doing a firing run, you will see that the gun always indexes to a fixed loading position. This way, the loader doesn’t have to chase a moving breech. Abrams, not so much. There is an ‘Elevation uncouple’ switch the loader can trip to freeze the gun in position, but it’s an extra step and doesn’t help if the gun is in a particularly awkward position, such as in max depression.

 And, of course, there are the safety issues. One starts to see more of a proliferation of safety devices, such as recoil guards for the commander. It becomes so much easier to, as the report observes, accidentally get thrown into the recoil path of the breech by an unfortunately times lurch of the vehicle. 

As ever, my Facebook page remains here, my Youtube channel here, and Twitch stream (Every Tuesday, and occasional evenings) is here.

And so, to a very stable Bob to take you, on the move, to the forum thread.