Trunnions on the Move

Advantages and Disadvantages of the Tank Turret The advantage of the turret is that it allows the gun to be traversed round the vehicle through the full 360 degrees, even when the tank becomes bogged down or has its suspension destroyed by mines. With its gun carried in a turret, the tank is able to switch rapidly from target to target over wide arcs both in the defense and also in the attack. It can remain in concealment, tracking an approaching target before suddenly opening fire. The turret gives the tank great tactical flexibility and is a method of gun mounting which has proven itself with tank crewmen. In a turret, the tank commander has all-round surveillance vision from the highest point of the vehicle, so that on the battlefield, he can form an appreciation of what is going on around him. The turret also provides full protection for the gun’s breech system and allows reloading to be carried out under armor. The conventional turret also allows crewmen hand access to the breech of the gun, to the firing system, and to the automatic loading mechanism, if such a system has been provided. But the tank turret presents a large target to enemy return fire, both when the tank is exposed in open country and also when it is engaging from behind cover. The height of the turret can be reduced by restricting the headroom made available to the loader, by requiring him to load seated or, finally, by eliminating him entirely and introducing automatic loading. The height of the turret roof above the gun trunnions is determined by the position of the recoiled breech of the gun when at full depression, so the 10 degrees of depression which are normally provided will raise it considerably. The width of the turret’s silhouette has recently been significantly increased by the addition of compound armor. This has made it both more easily spotted and also more easily hit by the enemy. Editor’s Note: For many years, ARMOR has published speculative articles analyzing possible future tank designs. While these articles are often somewhat technical and theoretical, it is important for soldiers who employ tanks to understand the thinking of the engineers who design them. Robin Fletcher, the author of this article, contends that the conventional turreted tank has reached a developmental dead end. In this first part of a two-part presentation, he details the problem. In our next issue, he willdescribe two ”gun-over-hull” designs that could solve many of the problems he identifies. With a conventional, turreted rear-engine design, the muzzle projects forward The weight on the gun trunnions - now some 4 tons in the case of a MBT - combined with the weight of the thick frontal armor, tends to throw the turret out of balance forward. Either this can be tolerated, as is Russian practice, and a powerful traverse system provided to overcome imbalance when firing on aside slope, or a bustle can be added at the rear of the turret to balance it. But this will increase the size of target presented to flank fire by the sides of the turret. The bustle can be used to accommodate radios, power traverse components and batteries, or can be sealed and fitted with blow-off panels to act as vented ammunition stowage (e.g., Abrams). Adding a bustle and compound armor to the outside of the turret increases the turret’s rotational inertia, reducing its ability to switch rapidly from target to target or requiring more power to maintain its same traversing performance. The tank gun is designed to have a short “inboard length” to the rear of the gun trunnions - a dimension of 55 inches is typical - but this, combined with the added space needed for recoil and reloading, in-trudes into the turret and effectively divides it into two parts while in action. When the gun is in full elevation, the gun intrudes downwards into the lower part of the fighting compartment - in fact, into the hull of the vehicle - requiring space to accommodate it (Figure 1). In a conventional turret mounting, the gun muzzle also projects a considerable distance in front of the turret, requiring a large arc to be clear of trees, buildings and other battlefield obstructions. Cross-country movement is made difficult by this forward projection of the gun muzzle and the turret may have to be traversed to one side or even to the rear to allow the tank-to surmount obstacles. Having reviewed the advantages and disadvantages of the conventional tank turret, attention can now be directed to steps which have ARMOR The Magazine of Mobile Warfare 33 already been taken, or which might be taken, to improve it. Improving the Tank Turret The Compact Turret was designed by Clifford Bradley in America in the 1960s. The tank commander was located immediately to the rear of the gun mounting and the gunner and the loader were lowered close to ring level so as to bring about a considerable reduction in the width of the target presented. This configuration was used in the American M60A2 mounting the Shillelagh 152-mm gun/missile launcher, now withdrawn from service. This type of turret was also proposed for mounting conventional, long-barreled high-velocity tank guns.l It can be criticized for failing to reduce the size of target presented to flank fire, but it did allow continued hand access to the breech of the gun and, most importantly, it maintained top vision - the ability of the tank commander to look all around him from the highest point of the vehicle. Recently, attention has been directed towards the so-called Flat Turret, which reduces turret height by allowing the recoiled breech to rise above the roof when the gun is depressed. A flap is to be opened in the roof to allow the breech to move upwards, in which case hand access may be able to be retained, but until details of this configuration become available, it is not possible to describe how sealing is to be maintained or urotection from overhead attack is to be provided.2 Alternatively, the gun can be carried and automatically loaded in a central cleft dividing the turret, with hand access only possible in an emergency. Rheinmetall of Germany, who have proposed this configurations, are aware that permanent separation of the two turret crewmen by this central cleft may be judged to be unacceptable and have, therefore, also put forward an alternative two-man turret, with the crewmen seated in tandem in the conventional manner and with automatic loading taking place from the other side of the gun mounting. This layout has been adopted by the recently announced FMC Armored Gun System shown at the AUSA Show in October 19854, but a bulkhead has been introduced between the two crew-Figure 2 Schematic shows relative position of trunnions on eleven vehicle designs. relative to a common 2-meter turret ring. men and the automatically loaded gun and they will only be able to reach it with difficulty. Both the Flat Turret and the Rheinmetall proposal reduce turret height and also target height when firing over a crestline with the former claiming to be able to do so with the gun still internally mounted while the latter admits to the gun having to be mounted externally.5 Several reasons - such as the addition of a muzzle brake, longer recoil to reduce trunnion pull and the need for space for autoloading at the rear of the gun - have led to a recent tendency for the gun trunnions to be moved forward of the front of the turret ring. This is by a small amount in the case of the Rheinmetall LPTS turret system, by a larger amount in the Royal Ordnance/Cadillac Gage low recoil turret6 and apparently even further in the case of the FMC Armored Gun System. If the usual 20 degrees of maximum elevation is to be maintained, this will lead to the trunnions being raised higher above ring level, which will raise the height of the roof of the turret and will also present a considerable blast trap under the front of the mounting (Figure 2). The American ARES 75mm automatic cannon is normally mounted with its center of gravity well forward of its trunnions, which are located so as to coincide with the weapon’s rotating chamber. Equilibration is then provided to balance the gun. This increases the gun’s forward projection, but decreases the intrusion of the gun mounting into the turret to such an extent that it is possible for the commander to be seated immediately behind the gun mounting, retaining his top vision.7 If this one remaining crewman could be removed from the turret and direct top vision was deliberately abandoned, the resulting “unmanned turret” could be controlled and sighted remotely by crewmen seated low in the hull.8 Given the short “inboard length” of the equilibrated ARES cannon, it could even be installed in a special, remotely-controlled, automatically-loaded turret on a ring only 54 inches in diameter.9 A similar unmanned turret in the experimental American Tank Test Bed (TTB) vehicle is controlled remotely by crewmen seated in the front of the hull.10 Loading arrangements, disclosed at the AUSA Show in Washington in 1983, showed rounds carried vertically, projectile downwards, in the turret basket below ring level. Each round is swung up to a horizontal position above the rear of the ring before being rammed forward into the breech. Direct top vision would, of course, have been sacrificed, as would hand access to the breech and to the loading mechanism, but the crewmen would be well-protected behind the increased armor on the front of the hull. These various arrangements - these improvements to the conven- 34 ARMOR The Magazine of Mobile Warfare tional tank turret - will not be able to reduce, and may actually increase, the forward projection of the gun muzzle, although they will probably reduce the turret’s rotational inertia. But these arrangements may divide the turret in two by the intrusion of the gun mounting, may even cause the gun to be externally mounted and, in seeking to expose the smallest possible target, may finally cause the tank commander to surrender his top vision. So an improved method of gun mounting is now needed and a major alteration of the position of the gun trunnions, relative to the turret ring, appears to be indicated. Relocation of the Gun Trunnions If the gun trunnions are moved from above the front of the turret ring to the rear, then the forward projection of the gun muzzle will be cut down, the turret will become much better balanced and its rotational inertia will be reduced. Also, the breech of the gun, and its associated recoil and loading space, will no longer intrude downwards into the turret ring and the lower part of the fighting compartment. Therefore, the crewmen will no longer be separated by the central gun mounting. If the gun is carried above the turret ring, perhaps in some form of cleft turret, then the crewmen will be able to maintain contact, or even to change places, beneath the shallow cleft. More specifically, this new trunnion position will be determined by the point of intersection of two lines, one the gun center line at full depression with the barrel justmak-ing contact with the front of the ring and the other the gun center line at full elevation with the rear part of the gun just contacting the rear of the ring. It is likely that the breech of the gun and its recoil and loading space will descend to below ring level at the rear of the ring when in full elevation, so it will be necessary to slope the rear hull deck armor downwards at an angle of 20 degrees to match the angle of maximum gun elevation. Note that this new trunnion position is bound to be higher above the ring than the old forward trunnion position. On an 85-inch ring, this increase in height will be some 10 inches. This is an admitted disadvantage of the 1 I.

I In the experimental British cleft-turret design of the 1950s. the loader fed rounds into a transfer mechanism. The rounds were automatically rammed forward after the gun approached the center-line of the hull (see also Figure 3, next page). proposed new rear trunnion position and will be considered more fully a bit later. However, instead of moving directly from the front trunnion position to the rear, let’s look at several intermediate solutions, each having its own advantages and disadvantages. If a large tank gun must be installed on a small turret ring, and the gun trunnions cannot be moved forward and equilibration is not acceptable, then the trunnions may be raised high above the front of the ring so that reloading is only possible out of the bustle at the rear of the turret. This has sometimes been referred to as a “gun-above-ring” mounting, although logically this designation should also be applied to all designs which adopt the rear trunnion position. They all confine the gun to above ring level. This configuration was used in the Russian KVII heavy tank and in some World War I1 artillery mountings. It was also used in the 1950s when the 20-pdr. tank gun was mounted on the Cromwell hull to create the Charioteer antitank vehicle, but elevation and depression had to be restricted to 10 degrees and 5 degrees, respectively, to contain the height of the turret.” This same type of mounting was also used experimentally to install a 120-mm gun on a Centurion hull to create FV4004 Conway.12 Although this configuration tends to create a very high turret, it does maintain crew access to the breech of the gun for hand loading and for the rectification of malfunctions and it also retains the tank commander’s direct top vision. The French oscillating turret occupies an intermediate position between front and rear trunnions. The hand-loaded FLll turret on the Panhard EBR 8-wheeled armored car placed the trunnions towards the front of the ring and used the upper part of the turret as a counterweight to the gun.13 The automatically-loaded FLlO turret of the French AMX-13 light tank, and the subsequent FL12 turret, with 105- mm gun, carried on the Austrian Kurassier tank destroyer,I4 located the trunnions further to the rear, just forward of the center of the ring, but limited elevation to 12 degrees to prevent the rear of the turret from making contact with the rear deck. Oscillating turrets were also tried experimentally on the American T-69, T-54 E land T- 77 medium tanks in the 19508, but were not put into production. The oscillating turret retains both hand access to the breech of the gun and also the tank commander’stop vision. Fives-Cail Babcock, its French designers, say that with their new FL20 turret, they can stabilize the complete upper part of the turret, and with it the gun, the crewmen themselves, and their vision devices.15 A third type of intermediate configuration places the gun trunnions at the new rear position, at the intersection of the gun center lines ARMOR: The Magazine of Mobile Warfare 35 when at full depression and full elevation, but will not insist on the rear of the hull being sloped downwards. Designs of this type enclose the breech of the gun and its recoil and loading space in armored protection, which has the effect of counterweighting the gun and causing it to move forward. This allows the turret to be installed - as was the French oscillating turret - upon a horizontally decked hull (Figure 3). The first turret of this configuration was the British cleft turret of about 1950, originally designed to be only lightly armored, which retained commander’stop vision and which was reloaded by one of two turret crewmen. He loaded rounds, base tirst, out of the rear of the turret into an armor-protected transfer mechanism, which then moved the round on to the gun center line and rammed it forward into the breech. Subsequently, this configuration was considered in a more heavily armored form with three turret crewmen during the development of the British Chieftain

The second example is the lightly armored Hispano-Suiza CNMP MARS turret recently developed in France. In this design, rounds are also passed individually, base first, into a rear armored box and then transferred to the breech of the gun.17 But in this case, the roof and the crew stations have been lowered to close above ring level, reducing the target presented to enemy fire, but at the same time sacrificing top vision. This is unlikely to be acceptable to the tank commander of a MBT who will fear that the enemy may observe the gun mounting above his vision devices before he is in a position to see the enemy. Although he may be provided with a tall panoramic periscope looking out above the highest point of the vehicle, he can only observe a narrow field at any time and he will fear that he will be surprised from another direction. This whole question of the surrender of direct top vision is of vital importance and will be discussed more fully, but here, it is sufficient to note that in the interest of weight saving and target reduction, top vision has been surrendered. Another example of this particular configuration can be found in American proposals made in 1980.+...,... I I ( I ‘ I

. I ’ Figure 3 British cleft turret on horizontally-decked rear-engined hull limits elevation to 15 degrees. Rounds are hand-loaded rearward into an armored box enclosing rear of gun, then mechanically rammed forward into the breech. for an ACVT Concept Vehicle mounting an ARES automatic cannon. As in the MARS turret, the turret top had been lowered to just above ring level and direct top vision abandoned.18 In this case, the abnormally short inboard length of the equilibrated automatic cannon allowed rounds to be loaded - not rearward as in the MARS turret - but straight upwards into the chamber. The turret could be carried on a hull which was not only horizontally decked, but which actually had raised rear hull deck armor. New Tank Gun Needed The tank gun will be in a very different situation when it is removed from the front of the conventional turret and relocated much further to the rear. No longer will its breech and its associated recoil and loading space be contained within turret armor. It will now project to the rear of the turret and above the rear of the hull of the vehicle. This will immediately allow the distance between the rear of the gun and its center of gravity to be increased to any length thought to be appropriate by lightening the breech ring assembly, by fitting a brake to the muzzle or by increasing the length of the barrel. And since the gun will now be in a “gun-above-ring” mounting, it will not intrude into the lower part of the fighting compartment and the two turret crewmen can be seated on either side of the gun mounting with close contact remaining possible between them. But with the breech now well to the rear of the turret, crewmen will no longer be able to reach it by hand. As a result, the reliability of remote operation will become of the greatest importance; and it is doubtful this can be achieved simply by depending upon recoil. In addition, some form of external power will be required for the automatic loader -which will then have become absolutely essential - and to download rounds back to ready-round stowage if the wrong type of round has been loaded. The breech system, now exposed, will be subject to direct small arms and splinter attack, making retention of the present sliding block breech system unlikely. The combination of these factors makes it probable that a lighter, power-operated, screw breech system will need to be provided, which when closed will become self-protecting. Such anew breech system may be combined with existing gun barrels or may form an integral part of a rearward barrel extension of an entirely new tank gun. Although it might be possible to employ existing rounds, using cases or at least stub cases, with case ejection taking place directly over the rear of the vehicle, this would probably only be used as an interim solution, giving way to parallel-sided fixed rounds of reduced length using completely combustible cases. A simple, cylindrical shape would be most easily handled in stowage and by the automatic loader, and combustible cases would leave no debris to give away the vehicle’s presence. Study of a variety of different unorthodox gun mountings shows that rounds will either approach the breech from the rear and be rammed forward into the chamber or they will be supplied from the direction of the gun trunnions and will then have to be moved a considerable distance rearward, to beyond the rear of the gun, before being returned forward. If, in this latter case, the gun could be divided 36 ARMOR. The Magazine of Mobile Warfare

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!...... I!: 1,... I.... __ -..___ Figure 4 In this design, a cleft turret on a front-engined hull, a controllable suspension system could help to elevate and depress the gun which would reduce both turret height and overall vehicle height. around the front of the chamber and its rear portion then inclined or moved sideways, it would become possible to load the parallel-sided rounds directly, base first, into the chamber in one simple rearward movement before reassembling the gun for firing. Such a "divisible gun" has recently been suggested for use in a turret which uses front trunnions,lS but it would be even more beneficial when the introduction of rear trunnions moves the rear of the gun well to the rear of the turret (Figure 4). The breech system of the present ARES automatic cannon makes it suitable for this type of treatment, with the chamber being moved to one side to be loaded instead of rotating. It is even conceivable that, in an emergency, rounds might be able to be hand-loaded into the chamber directly out of the rear of the turret. Thus, although a conventional tank gun can be employed initially - and, as has been seen, can be used with its breech system enclosed in an armored box above a horizontally decked hull (e.g. MARS turret) - anew tank gun system is now needed, probably with a power-operated screw breech system and with its center of gravity much further forward. This new gun system will have been specifically designed for installation upon rear-positioned gun trunnions and its introduction will allow the full potential of gun-above-ring mountings to be realized. Towards a New Turret System It is not being suggested that the conventional tank turret should be abandoned in favor of turret configurations which employ the proposed new rear trunnion position, but rather that the limitations of the former should be frankly acknowledged and the possibilities of the latter should be fully appreciated and exploited. The conventional turret may continue to be used in particular circumstances, where hand loading and hand access to the breech of the gun are considered essential. The disadvantages of the conventional front-trunnioned turret as regards muzzle forward projection, turret balance, rotational inertia and gun intrusion are now well-appreciated. These problems will be increased if a muzzle brake is added or if the length of the barrel is extended in order to increase muzzle velocity.20 If the trunnions are moved forward of the front of the turret ring, then turret height will be increased and so will the size of the blast trap under the front of the mounting. Raising the gun trunnions high above the front of the ring and reloading out of the bustle - as in the British Conway experimental vehicle - cannot be considered as a serious alternative because of the greatly increased height of the turret. Nor can the oscillating turret be favored if it has to be armored to MBT standards. Shoulda-FlatTurre?be adopted, there may be a sealing and protection problem or the gun may have to be mounted externally in a central cleft which will divide the turret. And an unmanned turret, as in the Tank Test Bed vehicle and in some ARES proposals, raises even greater problems of remote gun operation and would also require the provision and acceptance of some form of remote vision. The British cleft and the French MARS turrets, which are so dissimilar in the size of target which they present to enemy fire and in their top vision retained or surrendered, both adopt the new rear trunnion position. But both then have their guns advanced forward by the weight of their rear loading boxes. If this counterweighting effect is removed - as it should be in the interests of overall weight reduction - then the breech and its recoil and loading space will be moved much further rearward and will swing down to below ring level when the gun moves to full elevation. This will require that the roof at the rear of the hull will have to be sloped downward at some 20 degrees to match the maximum angle of gun elevation and indicates a clear preference for a hull layout which uses a front engine (e.g. Israeli Merkava MBT). Thus, with the exception of those turrets which adopt counterweighting - or, in the case of the ARES cannon, equilibration - to fit them for installation upon horizontally-decked hulls, there do not seem to be any acceptable compromise configurations lying between present conventional turrets which employ front trunnions and those which will adopt rear trunnions and a sloping roof at the rear of the hull. There is unlikely, therefore, to be a slow transition from front trunnions to rear through viable intermediate configurations, but rather an abruptrevolutionary change from one form of gun mounting to the other. And the new trunnion position will tend to be at a greater height above the ring, the breech end of the gun will be exposed to the rear of the turret, and automatic loading will have become quite essential. Mounting the Gun on a Tank Now that we have considered the relocation of the gun trunnions relative to the turret ring, let us develop the same theme even further and consider the mounting of the gun not just in relation to the ring, but in a wider context, with direct reference to the tracked hull of the vehicle. More specifically it would be the front and the rear of the top run of the tracks that would form the reference points. The gun would then be located centrally and symmetrically above the hull of the vehicle, whose length it would match closely, and a va- ARMOR: The Magazine of Mobile Warfare 37 riety of different gun mountings would be introduced between the gun and the hull to provide elevation and traverse. Many different methods of mounting the gun have been proposed or could be suggested and they will now be grouped and reviewed in three separate series to discover which will prove the most suitable.

I. Casemate Configuration The first type of mounting in which the gun might be carried is often referred to as the “kasematt-panzer” or “casemate” configuration. The crew is not mounted in a turret at all, but occupies fixed hull crew stations. But, following the theme of the rearward movement of the gun trunnions, designs that.mount the gun in the front of the hull, as in Jagdpanzer Kanone,21 or in more heavily armored vehicles similar to the Jagdpanther of WWII,22 will be rejected in favor of designs that move the gun much further rearward and centralize it above the hull of the vehicle. One example of this type is the unique Swedish ‘S’ Tank, built in the 1960s. Its gun is fixed not on, but actually within its hull, which aligns the gun on the target by tipping the complete vehicle back and forth on a controllable suspension system and traverses it by the differential action of its tracks. Other nations were unwilling to accept this as a valid MBT configuration: they did not like having to turn the complete vehicle to engage targets to right or left, found it difficult to track moving targets, and discovered that although the ‘S’ Tank could be developed to fire on the move, this could only take place in the vehicle’s direction of travel. But the ‘S’ Tank configuration still remains one of the available options: its clean, compact shape argues in favor of its adoption if vehicles must be of reduced signature and are to be clad in reactive armor against the increasing threat of overhead attack. The ‘S’ Tank, like the conventionally-turreted tank, has the im-. portant advantage of retaining direct crew surveillance vision at the highest point of the vehicle. Its overall height should be less than that of the turreted tank and the target which it presents when firing over a crestline is low but is of considerable width if measured to - + -

- Casemate tank with limited traverse on gun trunnions over the rear of the hull. Figure 5 Casemate Tank with UDES-17-type “lift-and-turn” mounting and 360- degree traverse. Casemate Configurations the outside of the track guards. Since there is no relative movement between the gun and the hull, the automatic loading system can be comparatively simple, and with the gun contained within the hull, there is access to the breech and to the autoloader if it malfunctions. It has often been suggested that the short length of track on ground, which causes the ‘S’ Tank to pitch during cross-country movement, could be avoided by mounting the gun on trunnions outside the hull armor and providing it with elevation and depression. This could simplify the vehicle’s suspension but would require a more complicated loading system and some form of breech armoring. The infinitely variable steering system, however, would still be required for gun traverse. Modification might be carried even further by providing some measure of limited traverse. While this would allow it to fine-lay and to follow moving targets without having to traverse the complete vehicle, it would also lead to a more complicated gun mounting and loading system. Rheinmetall of Germany showed an illustration of such a vehicle at the 1983 AUSA Show,23 with an automatically-loaded low-recoil 105-mm tank gun camed on an 8x8 armored hull with two k e d crew stations, one on either side of the gun mounting. An even more advanced gun mounting system can be introduced based on the Swedish UDES- 17 design, proposed in the late 1970s (Figure 5.). Here, the gun was to have been carried externally but lowered between two fixed hull crew stations. When ready to fire, it could then be raised and traversed to engage flank targets.24 This particular “lift-and-turn” mounting had to return to the 12 o’clock position and be lowered again to be reloaded, then raised again and traversed back onto- the target. Such a gun mounting configuration can retain direct crew ‘top vision’ up until the moment the gun is raised, but the repeated traversing and re-traversing of the gun to fire each individual round could give away the vehicle’s position.

11. The Overhead Gun The overhead gun has long held a fascination for tank designers because the gun mounting will pre- 38 ARMOR: The Magazine of Mobile Warfare sent only a very small target when firing over a crestline and because the weight saved by reducing or eliminating the turret can be applied as additional armor on the hull front. This configuration can be approached by a final development of the front-trunnioned tank turret to become an unmanned turret, as in the American Tank Test Bed vehicle.25 Alternatively, an externally mounted gun can be placed above a turret ring or on a pillar mounting, which would be of reduced diameter and might have bearings both in the roof armor and also in the floor of the hull (Figure 6). The TTB employs an automatic loader originally intended for a manned tank turret. The human loader would have been superseded by a loading system which would have raised rounds to above the rear of the ring and then loaded them forward into the gun. Moving the two remaining turret crewmen down into the hull will leave the gun still internally mounted within turret armor, but although the breech will swing down into the hull on elevation, they may not be able to reach it to rectify malfunctions.26 The more radical overhead external gun configuration, which cames the gun above a ring or on a pillar mounting, may be held to have originated with the British test bed vehicle constructed in the late 1 9 6 0. Similar designs have been produced more recently in Germany and in Sweden, based on the hull of the Marder MICV, with the German vehicle bearing the designation VT S-1.28 Several different problems arise, particularly when the latter configuration is adopted. The first is that the gun mounting will remain fully exposed some distance above the hull of the vehicle, givingrise to the two separate problems of ‘prominence’ and vulnerability. The prominence arises from the fact that the full 20-foot length of the gun will form a straight line well above the roof of the vehicle to stand out as a discontinuity above whatever cover it may be occupying. The small target presented by the front of the gun will reduce the chance of the enemy being able to hit it and the addition of a small amount of armor may be able to provide protection, at least against return fire Dverhead gun internally mounted in In unmanned turret (TTB Vehicle). Overhead gun externally mounted, ain the Swedish UDES-19. Figure 6 Overhead Gun Configurations from the particular target which it is engaging. But the gun and its mounting will have to be able to withstand enemy fire not only from straight ahead but also from other directions. Protection from small arms fire and splinter attack should be possible, particularly if a screw-breech or a divisible gun has been provided, but the mounting and the sighting system will also need to be protected. The transfer of rounds to the gun from the hull of the vehicle provides the second set of problems, and the automatic loading system itself may also need protecting. Rounds may not be able to be supplied from the direction of the gun trunnions because of the small diameter of the gun mounting pillar but may have to be raised up from the rear of the hull and loaded into the breech from that direction. This may only be possible when the gun is in the 12 o’clock position, but more advanced systems, such as that used by the Swedish UDES-19 design, are able to transfer and load rounds whatever the gun’s elevation and travere. S An alternative is to carry at least a proportion of rounds on the gun itself, where reloading will be easily accomplished, and then to recharge this ready-round magazine from hull stowage during a break in the action. The disadvantage of such a configuration is that this “firepower pack” will be bound to have larger dimensions and enemy fire will, therefore, be more likely to hit it.30 With both the unmanned turret and the overhead external gun mounting, crew vision remains the most intractable problem. By this, I don’t mean high power, high resolution vision for observation, target identification or sighting, but general all-round wide-angle surveillance vision where high resolution is not so necessary. Perhaps consideration of this problem can be refined further by saying that a package of remote vision sensors - ARMOR The Magazine of Mobile Warfare 39 can be mounted on top of the gun mounting. But more important is the presentation of their information to the tank commander in the vehicle's hull.31 Providing him with a single, fixed screen will not only restrict his field of view but may cause him to lose orientation - if not to become actually ill as the 'sensor head is rotated during crosscountry movement. Ideally, he should be surrounded by a screen onto which would be projected a stabilized image of the scene around the vehicle, giving him both wide-angle vision and also orientation. But space limitations may not allow this. An accceptable compromise might be to provide him with a helmet-mounted display, as in the AH-64 Apache attack helicopter, with the television or thermal-imaging sensor head driven by a helmet position sensing system. This would do nothing to increase his field of view, which would remain restricted, but would preserve his orientation by allowing this field to be turned instantly by natural head movement.32 So seriously regarded is this problem of crew 'top vision' that the experimental Swedish articulated tank destroyer UDES XX-20 seated the commander in a lightly armored capsule. This capsule could rise above the level of the gun mounting to reestablish direct wide-angle top vision.33 If this had to be done for an experimental antitank vehicle designed to engage only when stationary, how much more important will be direct top vision for a main battle tank committed to a war of maneuver? The American Surrogate Research Vehicle (SRV) has been constructed to study the problem of remote top vision,34 but until a Satisfactory solution is forthcoming, the overhead gun may be used for defensive or specialist vehicles but will not be accepted as the means of mounting the main armament of the main battle tank.

111. The Gun-Above-Ring Configuration The third series of gun mountings to be considered is composed of those in which the gun is drawn back above the turret ring, and does not, therefore, descend down into it. In this type of mounting, the crewmen move around with the gun to face in the direction of the target. In many respects, the French oscil-Above, side view of MPG system. a cleft turret design with conventional hand-loaded tank gun and suspension inclination. shown here at 5 degrees. t. '

.,

....... _..... View of turret at full depression ever crest. ' Figure 7 lating turret can be considered to have been the first of this series with the British cleft turret following closely behind it. In the French design, the trunnions are normally forward of the center of the ring, but the trunnions of the British turret are further to the rear. Earlier, I pointed out that the trunnion position of both are likely to be some 10 inches higher above the ring than on more conventional front trunnion turrets, including the recently developed flat turret. The size of target presented by a cleft turret can, of course, be reduced by lowering the two halves of the turret until the crewmen are looking out close above ring level. This was examined in several German experimental designs and has been adopted as the configuration of the French MARS turret. While the German mountings had ailhou-ettes similar to that of a true overhead gun, the French design used a conventional tank gun and enclosed its breech in an armored box, presenting a somewhat larger target. The MARS turret differs from the British cleft turret in quite deliberately giving up top vision, and so suffers the same vision problems as the series of gun mountings, already discussed, which use the overhead gun. The MARS turret may be an acceptable way of putting a big gun on a specialist light vehicle, but its lack of top vision makes it unsuitable for the more heavily armored main battle tank. The designer is thus faced with the problem that retention of direct top vision and reduction in the size of the target do not fit easily together. Since an acceptable remote surveillance vision system has not yet been developed, direct top vision must continue to be provided and effort must, therefore, be concentrated on reducing the size of the target. In the general case where the vehicle is fully exposed in open country, this will mean finding ways of reducing the height of the turret and reducing the overall height of the vehicle. In the particular case where the vehicle is engaging over cover, it will mean reducing the size of target which will be exposed over the crestline. One method of doing this is the controllable suspension system of the existing Japanese Type 74 MBT, in which 6.5 degrees of depression and 9.5 degrees of elevation available at the gun trunnions are augmented by the ability to incline the whole vehicle 6 degrees backwards and forwards and some 9 degrees sideways.35 In addition, the Type 74 can be lowered and raised on its suspension. This offsetting of depression lowers the height of the Type 74's front-trunnioned turret and of the whole vehicle. The same method could be used to reduce the turret and vehicle height of a rear-trunnioned cleft turret design. The degree of offset provided may be restricted by the desire both to keep the length of 40 ARMOR: The Magazine of Mobile Warfare track on ground to within normal limits and also to leave adequate depression and elevation about the trunnions to allow for gun stabilization. This type of cleft turret design would retain top vision and allow hand-loading of rounds, base first, out of the rear of the turret. Moreover, it would do so with a reduction in the present 10-inch height penalty and in the overall height of the vehicle (Figure 7). It would, of course, be possible to continue this process to the ultimate, so as to create a vehicle in which the gun would lie close above the turret ring in a very low turret. This turret would provide no depression or elevation. The gun would be depressed and elevated by means of a controllable suspension system and an active suspension might eventually be introduced to provide for the stabilization of the hull, the gun, the crew and their vision devices.36 Unlike the UDES- 17 lift-and-turn mounting, which requires the crew to raise the gun before traversing, this turret, with suspension control, could traverse discreetly prior to engaging. This somewhat theoretical configuration would be unusable if its gun were advanced forward as in a front-trunnioned turret because the muzzle would then hit the ground during cross-country movement. But if the gun were moved back, there would be no overhang and the vehicle could move cross-country without any restriction. An alternative is to adopt a gun mounting system similar to that of the American Elevated Kinetic Energy Weapon (ELKE) test bed, in which an ARES 75-mm automatic cannon is camed above the turret ring of a Sheridan hull.37 This ELKE vehicle can be considered as carrying its gun upon front trunnions and then lifting those trunnions on arms pivoted close to the rear of the ring. It should be noted that in this particular test vehicle, the gun is not actually able to descend to below the level of the surveillance vision devices. Therefore, the design sacrifices top vision. By rearranging the ELKE configuration - and in particular by moving from front to rear trunnions -it is possibleto imagine the gun camed on arms, or on a single central arm, pivoted just behind the front of the ring. If this raisable gun mounting is then placed in the! e Raisable gun in cleft turret. This MBT concept uses a divisible gun. 1 Figure 8 I! View of turret at full depression over crest. central cleft of a very low cleft turret, the gun can be camed lowered below crew vision devices and lie low across the top of the ring. The raising mechanism can then be activated to raise it to above the level of the vision devices, to restore its ability to depress, to elevate, and to allow it to fire. This raisable gun configuration preserves direct top vision until the instant that the gun is raised up to open fire. The design allows the turret to be traversed slowly with the gun held in its lowered position before being raised up to start the engagement. In its lowered position, the gun will lie centrally and symmetrically close to the top of the hull, giving a turret height which will be no greater than that of a front-trunnion flat turret, and a low overall vehicle height (Figure 8). This combination of a raisable gun in a rear trunnion cleft turret will allow the MBT to engage immediately whatever has been observed through its vision devices and gives it tactical advantages which are quite outstanding. A vehicle so equipped will not have to move forward and rearward when engaging over a crestline, but will remain in a turret-down position with only its vision devices exposed, then raise its gun, fire a shot and lower it again. The target exposed will be no larger than that displayed by an overhead gun, but the time of exposure will be significantly shortened. Since the gun will normally be camed - and reloading will take place -with the gun at or close to its fully-lowered position, a raisable gun will not suffer from the prominence of the permanently-raised overhead gun and the protection provided for it will be increased.38 It has been suggested that a raisable gun might be inaccurate due to play which might develop in its gun-raising linkage, but that is not in fact correct. Accuracy will depend only on the maintenance of the correct relationship between the gun - or, more particularly, its muzzle - and the gunsight mounted on the cradle which will then be observed remotely by the gunner. In the case of a cleft turret with the crewmen traversing round with the gun, this remote viewing can be by means of hard optics, as in the Improved TOW Vehicle and in the ELKE test bed, giving the best possible resolution. If the crewmen are not to traverse, as for instance in the UDES-17 configuration, television might have to be used, possibly with some loss of resolution, but with no degradation in the accuracy of gun laying. Future Gun Mountings Selection of the most suitable method of gun mounting will be very much a matter of opinion and will eventually be decided by crewmen's perceptions of how future direct-fire engagements are likely to be fought. So far, the only limita- ARMOR The Magazine of Mobile Warfare 41 tion to have been imposed is the crew’s need for surveillance vision. Because of problems of field of view and orientation when such vision must be exercised indirectly, it is unlikely that overhead gun configurations - the American TTB, German VT S-1, Swedish UDES-19 and the French MARS turret - will be adopted for use in the MBT. Should a solution to indirect surveillance vision eventually be discovered, then criticism of the overhead gun will be transferred to its other problems, such as its prominence, its vulnerability and its remote reloading. Compared to the raisable gun, the overhead gun will still have to move forward and rearward to engage over a crestline and its time of exposure will be much greater. In contrast, the raisable gun will be protected by the turret while it is lowered for reloading and will only be exposed when it is raised to be fired. Thus, even if its vision problems are eventually solved, the overhead gun will not necessarily be selected as the successor to the conventional turret. Its position will be challenged by -and should logically be conceded to - some form of raisable gun. The first series of mountings which might be selected for use by the main battle tank are those which can be described as being of the casemate type. Elevation, depression, and some degree of limited traverse might be included and the breech of the gun might be outside the armor at the vehicle’s rear. Such vehicles would still have to move forward and rearward to engage over a crestline and would present targets which might be low but could also be quite wide. The attraction of this group of vehicles lies in the comparative simplicity of their construction and in their compactness. Although traverse would remain restricted, this group merits careful attention and may be about to receive renewed study as opinion hardens against the conventionally turreted tank. The UDES-17 type lift-and-turn mounting, although of the same origin, creates anew category of its own by using a raisable gun mounting to achieve all-round traverse while its crewmen remain seated in the hull. It is probable that ready rounds would be carried in the gun mounting to allow the gun, once raised and traversed, to continue Some Real-World Examples k The Swedish “S” Tank, a 1960s design, exemplifies one type of casemate configuration. with the main gun fixed within the hull. The Teledyne Armored Gun System proposal placescrew in the hull beneath a gun which presents a very small target when fired from behind cover. Shown being tested hereon a Sheridan chassis, the Elevated Kinetic Energy Weapon (ELKE) featuresgun trunnionsthat go up on pivoting arms mounted at the turret rear. firing until the target had been destroyed. The gun will form a small target when firing over a crestline, but its time of exposure will, of necessity, be longer than that of the ring-mounted raisable gun. The second series of mountings which might be selected is that based on the gun-above-ring cleft turret, with its height reduced either by inclination of the suspension or by the use of a raisable gun. Suspension inclination and the raising and lowering of the gun can thus be seen as two alternative methods available to lower the gun relative to the ring, and in the wider context, to lower it relative to the top run of the vehicle’s tracks. Although suspension inclination can reduce both turret and vehicle height, it can do little to reduce the size of the target presented when engaging over a crestline or to remove the necessity for the vehicle to move forward and rearward in action. If the vehicle could also be raised and lowered on its suspension, it could more easily be concealed, but if this ability were then to be deliberately employed to facilitate engagement over a crest, the operation might be only slowly performed and the size of target exposed would still remain large. Although total transfer of depression and elevation to the suspension system is certainly possible, and has already been discussed, it is more likely to be limited to some intermediate amount. 42 ARMOR The Magazine of Mobile Warfare

If, alternatively, the decision is taken to adopt a raisable gun mounting, there will be no point in introducing it to a limited extent. The gun must be lifted from below the crew’s vision devices to above them in one rapid movement so that direct all-round surveillance vision can be exercised in either case. Intermediate positions, giving reduced depression and elevation, could be used when firing in open country, but the full extent of gun raising would remain available and would be employed for stabilized fire on the move. A raisable gun mounting will create a gun-above-ring cleft turret of minimum height and the overall height of the vehicle can be reduced subject only to the provision of adequate volume within the hull. Compared to a vehicle employing suspension control, the size of target when engaging over a crestline will be reduced, the time of exposure will be much less and no vehicle movement will be required. Although consideration of these various gun mountings has so far been in terms of the MBT, they can equally well be applied to the MPGS - now the Armored Gun System. The advantages of a front-engined vehicle with its gun drawn back above its hull can be realized in place of the muzzle-forward projection of rear-engined vehicles using front-trunnioned turrets. It is claimed that the recently announced Teledyne Armored Gun System with an Overhead Gun on a front-engined hull has about the same chances of survival as the heavily armored M1 Abrams tank when in a hull-down position because of the much smaller target which it will present.39 It would be reasonable to assume that an AGS which was built to carry a raisable gun would be even better as the small target would only be exposed for a very In the case of an IFV-type vehicle, the cannon turret must often be raised on a spacer ring in order to give the angle of depression which is required.40 Adoption of a raisable mounting will allow the cannon to be camed close above the roof of the hull in a cleft turret of minimum height and then to be raised to achieve depression when required to open fire. To allow these selected gun mountings to be constructed, development programs for anew gun system, automatic loading, suspension control and gun raising will have to be initiated. But a major effort will also need to be directed to the development of a front-engined hull to allow the tank gun to be moved rearward, not only over the ring, but also with respect to the top run of the vehicle’s tracks. T h e cea-tion of such gun-above-hull tanks will be the subject of my concluding article in the next issue of ARMOR. limited time. Footnotes I R. P. Hunnicut, Patton - A History of the American Main Battle Tank, Presidio Press, 1984, p. 179. 2 Wolfgang Mathos, Rolf Hilmes,“TheLeop-ard 3 Debated,” Military Technology, No. 10, October 1984, p. 85. 3 B. Sauenvein-Reznicek. “New Rheinmetall 105-mm Gun on Mowag Shark Wheeled Armoured Vehicle,” IDR, No. 7, July 1982, p. 929. 4 Ramon Lopez, “CCVL Tank Unveiled,” ZDR, September 1985, p. 1389. 5 Rheinmetall, “Lightweight Protected Turret Systems (LPTS)” (Brochure), AUSA Show, Washington, 1984. 6 Royal Ordnance, “Weapon Systems for Armoured Fighting Vehicles” (Brochure), British Army Equipment Exhibition, Aldershot, 1984. 7 Christopher Foss, “AAI Corporation RDF Light Tank with Universal Turret,”Jane’s Armour and Artillery 1984-85, p. 154. Ibid., p. 153. 9 ARES Inc., “75mm Universal Turret System” (Brochure), USMC Show, Washington, 1984. 10 Philip Bolte’, “Tank Technology in the USA,” Defence Attache’, No. 3, 1984, p. 17. 11 Christopher Foss, “Charioteer Tank D e stroyer,” Jane’s Armour and Artillery 1979-80, p. 73. 12 RAC Tank Museum, “Conway (FV4004) - 120-mm L1 on Centurion 3,” British Tanks 1946-1970, p. 45. 13 Christopher Foss, “Panhard EBR Heavy Armoured Car,” Jane’s Armour and Artillery 1984-85, p. 166. I4 R. M. Ogorkiewicz, “Steyr Armoured Vehicles,” ZDR, April 1982, p. 465. 15 D. H. C. Jenkins, “Fives-Cail Babcyk Introduces a New Oscillating Turret, ZDR, March 1985, p. 411. 16George Forty, Modern Combat Vehicles - I Chieftain, Ian Allen Ltd., in particular, the first chapter, written by Leslie Monger, MBE. I 7 Christopher Foss, “Hispano-Suiza CNMP 90-mm MARS Turret,” Jane’s Armour and Artillery 1984-85, p. 767. l a Col. Lawrence B. Fitzmorris, “Developing Tomorrow’s Combat Vehicles,” ARMOR, MayJune 1980, p. 25. l9 Roger Smith, “What is a Tank?” (Reference to Hall’s carbine), ARMOR, September-October 1984. 2o Eric C. Ludvigsen, “Army Weaponry - Lengthening the M68 105-mm Tank Gun,” Association of the US. Army Green Book, 1984-85, p. 457. 21 Christopher Foss, “Jagdpanzer Kanone SP Antitank Gun,” Jane’s Armour and Artillery 1984-85, p. 428. 22 Paul-Werner Krapke, “A Design Concept for a Heavy Tank Destroyer,” IDR, March 1983, p. 341. 23 Rupert Pengelley, “Report on AUSA ’83 - 105-mm SLR Gun on Piranha 8x8” (an illustration), Defence Attache‘, No. 6,1983, p. 60. 24 D. H. C. Jenkins, “New Concepts in AFVs -The Swedish Approach,”ZDR, 12 December 1982, p. 1720. 25 Hoeltzel, Sawka and Cag, “Tank Test Bed Vehicle,” Army Research Development and Acquisition Magazine, November-December 1982, p. 19. 26 D. H. C. Jenkins, “Autoloading - The U. S. View,” IDR, 7 July 1984, p. 909. 27 R. M. Ogorkiewicz, “Tank Test Beds” (The COMRES 75 t e s t vehicle - photo), ARMOR, March-April 1984, p. 18. 2 R Hans Rudolf Lembcke, “A Tank of the Future in the Context of German Defence Technology - VT S-1,” Krupp MaK Defence Journal, No. 5 of November 1980. 29 D. H. C. Jenkins, “Autoloading in Tanks,” IDR, 7 July 1984, p. 907. 30 Dip].-Ing. Erich Drosen, “Automatische laden der panzerkanone,” Soldat und Technik, 10 October 1983, p. 545. 3l Philip Johnson, “Tank Vision Systems of the Future,” Military Technology, No. 6, June 1984, p. 49. 32 Robin Fletcher, “From Tank Turret to Overhead Gun,” ZDR, January 1984, p. 49. 33 Christopher Ross, “Swedish Tank Destroyer Developments - UDES XX-20” (Photos), Jane’s Armour and Artillery 1984-85, p. 434. 34 Philip Bolte‘, “Tank Technology in the USA,” Defence Attache’, No. 3, 1984, p. 17. 35 Christopher Foss, “Japanese Type 74 MBT,” Jane’s Armour and Artillery 1984-85, p. 45. 36 Peter Massey, “Active Suspension,” ARMOR, September-October 1979, p. 35. 37 PACCAR, “Elevated Kinetic Energy Weapon Test Bed (ELKE)” (Brochure), AUSA Show, Washington, 1983. 38 Robin Fletcher, “Hit Avoidance and the Tank Gun,” IDR, May 1984, p. 598. ROBIN FLETCHER was commissioned in the Westminster Dragoons in 1941 and later served in the Special Operations Executive and 2d Special Air Service Regiment. After the war, he attended the technical staff officer’s course at Shrivenham, spent two years on tank design at Chobham, and returned to Shrivenham to lectureon tank armament. After leaving the service, he raised crops in Kenya and cattle in Ireland. His articles on armor have been published in Internation-alDefense Review, Soldat und Technik, TANK, and other journals. ARMOR. The Magazine of Mobile Warfare 43