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The Chieftain's Hatch: Centurion III Pt 3

This is the third in a series of four articles about the US’s evaluation of early Centurion tanks. Part 1 is here, part 2 here. This third one has been delayed for a couple of reasons. Firstly, frankly, I’ve been a tad busy. Secondly, the report on Centurion II’s fire control system is pretty much a wall of text. Not a single graph or picture to it, making assessing the 28-page report a little difficult. Ultimately, there is no real way around it, this will be one of the most boring Hatch articles ever. Feel free to skip this one, and come back the following week for the ‘lessons learned’ article.

If you’re not familiar with US report systems, they follow a fairly standard format, in which the first couple of pages are a background overview and a superficial overview of the results. The details are found in the appendices, which can be many pages long. Unfortunately, in this case, there’s as much overview as there is detail, so I’ll try picking a few bits here and there, linking to the ‘meat’ of the tests in a PDF, and then do a quick personal assessment.

So, onwards.


a. The Centurion II, mounting a 17-pounder gun, is the forerunner of the Centurion III which mounts a more powerful weapon, the 20-pounder gun. The two tanks are identical except for their main armament and certain modifications incorporated in the latter. The secondary armament of the Centurions consists of a coaxially mounted 7.92-mm Besa machine gun. Four men comprise the crew. The driver's compartment is located in the right-hand, front corner of the hull. The left, forward portion of the hull is utilized for ammunition stowage. The remainder of the crew operate within the fighting compartment, the loader being on the left of the main armament.

b. The gun control systems provide manual traverse and elevation, non-stabilized power traverse and manual elevation, stabilized power traverse and elevation, and emergency traverse at a fixed rate. Powered control is accomplished by the Metropolitan-Vickers all-electric gun control system in which, when desired, stabilization in azimuth and elevation is effected in relation to the rate at which the turret and gun are disturbed by vehicular movements. The primary direct fire control equipment consists of a range gear and periscopic sight which, together, permit mechanical adjustment of range and axial aiming in elevation. Firing can be carried out electrically or mechanically.

BACKGROUND. The prototype of the Metrovick gun control system, installed in a Centurion II, underwent preliminary testing in 1946. Operational and acceptance tests, using production equipment, followed in 1947. Currently, the Metrovick system is standard with all Centurion II and III tanks. Nevertheless, refinement of the components has continued. Minor modifications were made in 1948in order to improve reliability and efficiency. The test item as installed by this board includes those improvements. This board was directed to service test the Metrovick system for possible application to US tanks.


a. Ease of installation and adjustment investigations were carried out in conjunction with refitting and repairing the gun control system and its related mechanical components. The resultant experience demonstratedthat turretcomponents must be designed and mounted to facilitate installation, adjustment, and unit replacement. The Metrovick system was deficient in these respects, having an excessive number of separate components, especially external cables, all of which were relatively inaccessible. This slowed up not only the physical fitting of the equipment but also the substitution of individual components when carrying out unit replacement procedures. This complexity, in addition, made trouble shooting exceedinglydifficult. Furthermore, the proper functioning of the system depended on the precise adjustment of a number of interrelated controls. Setting up, consequently, was a tedious process and required the services of highly trained personnel. Moreover, this initial adjustment was usually voided when certain key component parts were replaced, necessitating setting up the system again. Operational trimming of the system, on the other hand, was a relatively simple process. It is believed that the deficiencies cited above are a question of design and capable of correction. Projected improvements listed in subparagraph d (3) should greatly simplify adjusting thesystem in its entirety.

b. The electrical gun control system, despite deficiencies known to be present, was subjected to intermittent use for a total of 36½ hours between 2 February 1949 and 16 December 1949, a period of 10½ months. During this time the equipment received only routine care and underwent periods of prolonged operation. Nevertheless, the system functioned without abreak-down until mid-December, at which time the traverse gyro failed and had to be replaced. However, judging by experience with the Centurion III, an excessive number of amplifier trims (nine) had to be carried out. This was attributed, at least in part, to misalignment of the elevating gear and to the undetected presence of a. faulty traverse friction switch.

c. Limited moving-vehicle firing tests were conducted. In part, this was dictated by circumstances. Comprehensive testing, although originally scheduled, appeared pointless in view of the difficulties involved in drawing subsequent comparisons with US developments which are to be tested on different courses and with different crews. As a result, an abbreviated stabilized firing program, sufficient to check the effectiveness of firing on the move with the Centurion II, was carried out to determine whether or not it was worthwhile to utilize the British tank in comparative testing at a later date. Results obtained confirmed the worth of the Metrovickstabilizer.

(1) In continuous, head-on runs, closing from 1,500 to 500 yards at average speeds of 8 to 15 miles per hour, 80 percent effectiveness was achieved with shell HE; the number of target effects equaled the number of actual hits. Fifty-five percent of the hits were obtained with 17-pounder shot APCBC on 12- x 12-foot panels during similar runs. The average firing range was approximately 950 yards and, as a rule, the majority of the hits were experienced at ranges short of 1,150 yards. It should be noted that the initial and subsequent ranges were known to the tank commander when the aforementioned firing was carried out. In later firing, only the initial range was known and changes thereafter were based on visual estimates. Under the latter conditions, 83 percent hits and target effects were obtained with 90-mm and l7-pounder shell HE in halting-to-fire engagements using hand elevation and straight power traverse. The same crew, again relying mainly on estimated range data achieved 64 percent hits and target effects with 17-pounder shell HE on nonstop, stabilized runs over the same course and against the same targets. 

 (2) In the halting-to-fire runs, the minimum standstill time for one shot was 10 seconds, the average being closer to 13 or 14 seconds. The interva1 between moving out and the first shot and between subsequent shots in continuous runs varied widely, the shortest experienced being 5 seconds. The rate of fire, as well as the accuracy, was, of course, directly affected bythe nature of the terrain and the speed and adeptness with which it was negotiated.

 (3) Under the conditions of the test, the firing interval on nonstop runs was 10 seconds, or less in 30 percent of the instances and was 15 seconds, or under, in 50 percent of the time. On the nonstop runs, the average tank speed was 10 percent higher than the average speed, exclusive of halts, attained on the stopping-to-fire runs. The elapsed time on a given course was 70 percent less for the tank which fired on the move than that for the tank which halted to fire five times in the same distance.

d. The current US tank-development program calls for stabilization, in azimuth and elevation, of the main armament of the new light and medium tanks. In addition, each of these tanks is to be supplied with a built-in range finder and computing mechanism. The flow of range datato the computer is to be automatic and the computer, in turn, is to resolve input data and automatically apply superelevation and lead angle to the gun.

 (1)The Metrovick system, being of the rate-responsive type and utilizing constrained gyros, may not be suitable for use with fire control devices presently envisaged. A stabilizer employing one or more positional gyros will probably insure greater efficiency. In any event, the Metrovick unit has no provisions for the automatic application of superelevation and lead angle to the gun.

 (2) The test stabilizer, however, is adequate for use with conventional sighting equipment wherein superelevation, for instance, is obtained by altering the line of sight. Nevertheless, there are practical limitations to utilizing the Metrovick equipment. In the first place, its use is contingent on the provision of a balanced gun mounting. Secondly, its operation is dependent on related mechanical components, principally the elevating gear and the traverse gearbox, which would be difficult to fit into a turret for which they were not designed. Lastly, the British stabilizer in its present form consists of numerous and, in some cases, bulky components; the limited space in US turrets would cause a hardship.

 (3) Despite the foregoing, it appears unrealistic at this time to regard the Metrovick system as out of date or to eliminate it from further consideration, especially since the merits and demerits of a fully integrated system of fire control have not been established and US development-type fighting compartments are as yet unproven by service testing. Moreover, it is conceivable that circumstances,including logistical factors, may force suspension of the requirement for fully integrated fighting compartments, at least for a certain class of tank. In such an eventuality, the Metrovick gun control system, which is aproven item, might prove acceptable, particularly if the following projected improvements are carried to a successful completion.

 (a) The first embraces modification of three major components and is designed to reduce the instability of the traverse servo system and to simplify and quicken the setting up or adjusting of the stabilizing system.

(b) The second modification affects the dampening unit in the gyroscopes end is intended to assist in maintaining a constant dampening figure and to increase reliability.

(c) It is also understood that the present Metrovick system is being redesigned in order to reduce the number of separate components, especially external cables, and to reduce its bulk.

 e. It was found that, at least from a user's viewpoint, it is difficult to isolate the performance of a stabilizing system from the performance of its associated equipment. In this connection it should be noted that reference 2a above [Parts 1 and 2 of this series – Chieftain], contains an evaluation of the fighting compartment components common to the Centurion II and III. It was also discovered that both the rate and accuracy of fireon the move were affected by the operating conditions encountered in a moving tank and by other factors not present when firing from a stationary platform. Crew efficiency, for example, was noticeably lessened as a result of the random motions of the tank. In fact, in view of the crew's resultant inadequacy under certain conditions, it appeared that there might be a practical limit to stabilizing accuracy insofar as tank armament is concerned. At the same time, it was evident that conventional fighting compartments did not represent an optimum asfar as fightability on the move was concerned end that the adverse operating conditions, which are to be expected in a moving vehicle, could be tempered considerably by providing suitable crew facilities.

 f. It was forcefully demonstrated, as a result of experience with the Centurion II, that the successful solution of the gunnery problems arising when firing on the move required the concerted efforts of two crew members, the gunner and the tank commander. It proved impractical for the commander to turn the execution of a fire order over to the gunner while he,the tank commander, carries out his command responsibilities.

 (1) Range and deflection errors were more prone to increase during a nonstop firing run than to decrease, as is the case when firing from astationary tank. Consequently, the gunner could not be expected to correct fire on the move without assistance since this forced him to cope not only with his initial errors in elevation and deflection but also with changes in those elements, especially in elevation, as the tank progressed on its course.

 (2) Of necessity, the commander established and applied the initial range, sensed the shot with respect to the target, and applied a corrected range on the basis ofthis sensing and the new position of the tank. The gunner, on the other hand, concentrated on aiming, firing, and correcting his sight picture, a pattern which was compatible with the characteristics of firing from a movingtank.

 (3) This experience disclosed no basis for believing that this two-man technique can be modified materially without sacrificing firepower unless an automatic range-rate device can be provided or unless quick, optical ranging by the gunner proves to be feasible while under way.

 g. Special training aids were not considered for this idem of equipment since adoption is not recommended.

 h. A draft of this report was circulated to interested agencies for comment. Their comments are listed and discussed in Appendix F, Coordination.

 CONCLUSIONS. As a result of experience with the Metrovick stabilizer in the Centurion II, Army Field Forces Board No. 2 concludes that:

 a. The test item is adequate for tanks employing a balanced gun and fire control equipment similar to that in the Centurion II.

b The system will not permit the automatic application of input data resolved by a computer, to the gun in the form of superelevation and lead angle.

c. Neither a theoretical or direct comparison can be made between the Metrovick gun control system and United States’ systems until the latter have been service tested.

d. The Metrovick equipment, being of proven worth, should be considered for use in US tanks in the event that US development-type stabilizers are not successful.

e. The full effectiveness of stabilizing the main armament of a tank can only be realized by considering, in the design of the fighting compartment and its components, the problems peculiar to firing from a moving vehicle.

 RECOMMENDATIONS. Army Field Forces Board No. 2 recommends that

a. The Metrovick gun control system be considered a satisfactory installation for tanks which feature a balanced gun and a conventional fire control system.

b. A new Centurion III tank embodying the latest type stabilizer and modifications be furnished this board for further test, and the Centurion II be returned to United Kingdom control.

 H.H.D Heiberg

Colonel, Armor



So that's the overview. Here's some of the meaty data, in this PDF.

Chieftain's commentary.

It is interesting to observe how the US Army is learning about a technology which we take for granted today. Although the US had had stabiliser systems in its tanks for several years, by this point, they were of such dubious effectiveness that it was not uncommon for units in the field to simply remove them from the tanks, and, in theory at least, were an order of magnitude below the dual-axis stabilisation that the British had implemented into the Centurion. In practice, of course, the dual axis stabilisation still didn't provide a true fire-on-the-move capability, but it was certainly an improvement, at least at medium and close ranges. Until the advent of coincidentally-fired stabilised sights in the 1970s, as opposed to a stabilised gun, this would prove to be an elusive capability. Note that in the report above, even the theoretical advantage of the stabilised sight when firing from the short halt seems to be more conceptual than in fact, presumably the crew was conducting the full ranging process.

The two notable conclusions were the fact that gunning in such a tank as Centurion was now back to being a two-man process, no longer could the gunner be left to his own devices while the vehicle was moving. The other was the realisation that there was more to firing on the move than simply stabilising the gun, the entire crew needed to be stabilised. Part 4 of this series is the observations of the Armored Board on the difficulties of the crew when firing on the move.

As for the system itself, the other point to note is that the US had decided, basically, to skip a generation in stabilisation systems, by incorporating the ballistic computer into the system. In Centurion II, it was still necessary to manually apply the range and superelevation (The amount the gun has to aim above the sight-target line to counter the drop caused by gravity). The US Army wanted a system which would do this automatically, the gunner would just put pip on target and the system would take care of the rest. That this would prove to be easier typed than done, of course, they had no way of knowing at this point.

So, overall, the US generally liked Centurion. They appear to have considered it to be inferior to the new generation of tanks they were designing, but quite competent for an already-extant vehicle. Some features, like the tracks and transmission, they didn't like. Some, like the stabilisation system and general capability, they did. The engine power they deemed insufficient for the future tank. The entire evaluation process was more of a learning experience, learning some lessons, both good and bad, from the tank the British had built, it was never an attempt to comparatively rate the tank in order of preference.

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

Over to Bob.