Elements of Tank Design

To a tank crewman, a tank is a large complex track-laying vehicle that requires a great deal of maintenance, mounts a monstrous cannon, armored to resist battlefield threats, and capable of negotiating rough terrain and running over most obstacles. To an enemy foot soldier, an attacking tank is a large, awesome, noisy, frightening, invincible machine capable of instilling terror in spite of what his leaders have told him about the capabilities of his weapons against the “weaknesses” of the tank. To a tactical commander of armor units, a tank is the ideal instrument for employingmobilepro-tected firepower in the aggressive assault role so vital to offensive land combat. To a commander of combined arms, the tank is the centerpiece of land combat-the optimum combination of firepower, shock action, mobility and protection when employed with other close combat units. To a tank developer, a tank is, in essence, a response to certain demands created by a tactical role. These demands are functional and can generally be described by a set of requirements or system capabilities derived from the interaction of the threat, technology, and the intended operational concept, and can be related to design in terms of configuration and characteristics. To a force structure analyst or military economist, a tank is a unit of firepower, whose cost and performance can be quantified and assessed in realistic combat scenarios in comparison with other exist-ingsystems orpossible new systems in a force structure. A tank may be viewed by various people, but no one can question that this combination of firepower, mobility, protection, and shock action called a tank is the most effective instrument of aggressive assault in land warfare today, and will continue to be in the foreseeable future. Cliff Bradley Much study has gone into tank design since the first tank entered combat in the WW I Somme offensive. At least two books, R M. Ogorkiewicz’s Design and Development of Fighting Vehicles, and Richard E. Simpkin’s Tank Warfare, have discussed tank design in great detail. Obviously, while a magazine article cannot discuss all those tank design factors covered in the above books, it is possible to cover some of the basic fadors. Most writings on tank design stress those fadors that distinguish tanks from one another and focus primarily on engine power, armor, and main armament. There are, however, other perspectives that must be considered such as length-to-width ratios, ground-pressures, length limits, and width and height. The tank designer must be aware of these limitations when he reads the Staff Requirement (UK), Required Operations Characteristics (US) or Tactical Technical Requirement (USSR), that establishes the basic design of the tank,l plus those speciSc requirements peculiar to the desired tank. They generally do not specify how the fmished product will look nor how it will be built.2 Theoretically, a tank designer can start with a clean sheet of paper. In practice, however, there are several design constraints that will affect the tank design. Briefly stated, tankers desire a tank that can, with a single shot, kill any possible opponent at all possible combat ranges; that can survive a hit from any opponent at any angle of attack, at any range that can move rapidly across any type of terrain at the fastest possible speed, and have the greatest possible road range. Logisticians desire tanks that cost little, can be transported on a pickup truck, require little or no maintenance, and consume little fuel and ammuni- november-december 1983 35 tion. Unfortupately, it is not possible to accomplish all this in any single vehicle, and features must be traded off to produce a balanced tank design. Dimensions Width is perhaps the most critical dimension on a tank because it governs the tank's capability to move along highways, cross bridges, be transported, and maneuver. For example, special timbers had to be laid on WW 11 Bailey bridges to protect the bridge curbs from damage by M-26 Pershing tanks, which were 20.3 inches (516 mm) wider than the M-4 Shermans that acould traverse the spans with ease. The width of tank transporters, aircraft, and railroad cars also affect the design width of tanks. The USSR limits width of cargo transported by rail to 3,414 mm (134.4 in). This in turn establishes the maximum width of soviet tanks.3 The U. S. h y originally set a maximum width of 144 inches (3,658 mm) for the MI tank, which is now being produced with a width of 141 inches (3,588 mm). Factors influene ing the width specified by U. S. tank designers include the Berne Intema-tional Railway Gage, which prescribes a maximum width of 3,150 mm (124 inches) or the maximum width of highway load limits, which generally range from 2,438 mm (96 in) to 2,591 mm. Both limits can be waived. The standard U. S. Army Heavy Equipment Transporter is 99.5 inches (2,438 mm) wide, but a transported tank overhangs each side. The limit of 144 inches specified in the original Material Need Document for the M1 was established as an arbitary, but reasonable, limit based on the most efficient use of space aboard cargo vesels. The width of a tank hull is also afected in part by the diameter of the turret ring.5 The turret ring must allow the gun breech to swing down to aim at an elevated target and must allow enough room for the gun to be loaded with along main gun round. Turret rings for U. S. tanks have varied in size from 60 inches (1,524.6 mm) for the M4 Sherman medium tank, mounb ing either a 75 or 76mm gun, to 85 inches (2,159mm) for the M-48 Patton and M-60 tanks mounting 9@ or 105 mm g u n s. 6 Table 1 gives the turret ring diameters for several tanks. Height. Three factors influence a tank's total height turret height, hull height, and ground clearance. If the overall height is controlled and kept low, the tank becomes harder to see and therefore harder to hit. A critical element in Soviet tank design has been controlling the height of the tank to reduce weight while maintaining the maximum level of protection with frontal armor. Reducing the height to the minimum has the most payoff in reducing weight because the frontal armor is thickest and requires more weight to maintain a given level of protedion.7 Therefore, if the height of a tank is lowered and if the weight is kept at a constant, the frontal armor can be thicker because it need not cover EI great an area Ground clearance is normally specified by the user, and for the US M60 tank is 18 inches (457 nunha The height of the hull is normally limited by the space required by the engine height and by the average height of 1 meter for the seated driver. The height of the turret is controlled by the size of the main gun and the main gun depression angle.s The turret roof height is also governed by the need for the loader to stand, and load main gun rounds. There must be at least 66 inches (1,676 mm) from the hull floor to the inside turret roof for the loader to stand. One method of determinin g the minimum height of the tank is to add the thickness of the turret roof armor, thickness of the flooring, thickness of the torsion bars (if used), thickness of the belly armor, and the ground clearance. An altema-tive method is to add the ground clearance, 40 inches (1,005 mm) for the seated driver, and 26 inches (660 mm) for the turret (additional space is always required for gun depression) to set a minimum height for a conventionally designed tank of about (2,122 This compares to a height of 94 inches (2,400 mm) for the Soviet Length. A tank's length is generally not as critical as its height or width. However, tank length is governed to some extent by tank width. The ability of a tank to turn is greatly influenced by the ratio of the length of the track on the ground to the width of the track If the ratio becomes too large, turning is impossible because forward thrust is offset by the power lost in the skid of the tracks. For tanks with simple transmissions having only one steering radius, the length to width (L/W) ratio should not exceed 1.5. Tanks with more sophisticated transmissions (with a variable turning radius) have L/W ratio limits ranghg from 1.7 to 1.8. The location of the tank's center of gravity (CG) has a major effect on the ability of a tank to cross obstacles. Ideally, the longitudinal CG should be located above the geometric center of the supporting tracks to create a uniform distribution of weight on the road wheels.ll T-62. Ground Pressure and Weight Perhaps one of the most critical factors affecting the mobility of tanks is the ground pressure of the tracks. The USSR sets a limit of 0.85 kg/cmz for dead (non-rubber bushed)tracklZ However, the Soviets have not fielded main battle tanks with a ground pressure greater than 0.81 kg/Cm2, including the T-64 and T-72, that have live track (table 2). U. S. tanks normally have higher ground pressure than do soviet tanks. Generally speaking, the lower the ground pressure, the easier-it is for a tank to travel over poor terrain. For example, the very low ground pressure of the British Scorpion armored fighting vehicles (0.35 kg/cmZ) allowed them to traverse very soft ground in the Falklands that was impassable to almost any other ground combat vehicle.13 The less the tank track pene trates into the ground, the less power is required to drive the tank. In addi- 36 november-december 1983 tion, softer s( as well as ha Allied to pressure is tl ern battle ta 39.6 to 60.6 tc It used to be 1 to less mobilil technology, ally have be tanks of low powerful eng does make it by rail or b also limit the use. The heavie its armor en\ As mentio design conk to reduce wei that requires armor protec areal densit) ideal properti are that it be hard, ductile, and stable16 Although titanium armor might be attractive from a weight point of view, it is much more expensive than steel Although aluminum is onethird lighter than steel, for an equal amount of protection it must be three times as thick as steel. This means that a steel armor hull and an aluminum armor hull giving equal protection would weigh the same. The thicker aluminum is also more rigid. However, aluminum armor can significantly reduce overall structure weight because an aluminum hull requires less reinforcement than does a steel hull. Aluminum is therefore very suitable for lighter vehicles. Chobham armor recently developed in the United Kingdom givea mgnifi-cantly better protedion, weighbfor-Thus, the heaviest armor is on the frontal arc,’* and the area that is normally most heavily proteded is the 6Ckdegree frontal arc.lg Figure 1 illustrates some of the 6Odegree arca that are possible on tanks. Due to weight considerations, most tanks would place the centerline of the 6Odegree arc at the rear of, or tangential to, the turret. The protection provided by a given thickness of armor is enhanced by sloping the armor to increase its effective thickness (figure 2).20,21 Additionally, greater angles of obliquity will heighten the chances for attacking projectiles to ricochet. Armor also offers radiation protection. Unclassified literature offers little data on neutron degradation tion comes from fallout or induced (secondary) radiation. Table 4 shows how different materials shield against radiation. It can be seen that steel is the most effective radiation shield. Using the formula K=V/2 X VP where K=the degree of gamma activity, V=the thickness of the material and VP=the half value layer, it can be seen that 1.5 inches (38 mm) of steel drops the level of radiation to one half, 3 inches (76-mm) to onequarter and 114-mm of steel to oneeighth.22 Thus, if one must be exposed to a nuclear attack, it is best to turn the front of the hull and turret toward the blast. Although recent advancea in armor have significantly improved protection, it is impossible to defeat every \ i \ /

\ i V

TANGENTI A t novern ber-december 1983 37 actual thickness cosineof angle of obliquity Equivalent thickness = 100 rnrn l00rnrn 100 rnrn cosine 60 degrees 100 rnrn 100rnrn 100 rnrn 1.5 3 2 292 rnrn

3. ET= cosine 70 degrees cosine 0 degrees ET = ET = ET = ET = 100 rnrn ET = 200 rnrn ET= Source: Tanks and Tank Troops, p. 94. Figure 2. Effect of sloping armor. possible threat. Armor alone is not the only factor to consider when evaluating a tank’s survivability. Survivability A tank should have protection against being destroyed even if the armor is penetrated. After a tank is penetrated, fire is the biggest hazard. Recognizing this, the Ml’s designers equipped it with seven sensors to detect a fire and extinguish the flame growth before it can cause an explosion. In older tanks with gasoline engines, the probability of fire was very high if there was a hit in the engine compartment or near a fuel tank. In such cases, the fire spread faster than would a diesel fuel fire. Additionally, vapors from a leaky gas tank were much more likely to cause a secondary explosion than were diesel fumes. Besides lowering the likelihood of fuel fires, and thereby improving survivability, the shift to diesels increased the tank’s mileage between refuelings. The gasoline-engined M-46 Patton tank had a range of 70 miles (113 km), while the M60Al (with increased fuel aboard) has a range of 300 miles (483 km).23 Ammunition propellent charges are the biggest fire hazard in the tank because they ignite instantaneously when struck by a pene trator. However, the risk of a propellant fire can be significantly reduced by using stowage racks filled with liquid, such as was done in the M-4 Sherman and the Chieftain. An alternate method is to use blow-off panels as in the M1.24 In addition to armor and fire protection, other measures that can enhance survivability include smoke grenade launchers or other smoke generating devices for screening purposes; self-entrenching devices that permit the tank to dig itself i q 2 5 and design features to lower visual, infrared, or audio signatures to protect against detection. Thus, the need for survivability helps determine how the tank is laid out. Tank Layout Tank layout (or how the engine, transmission, gun and crew are placed in the tank) is an example of form following function. A tank’s layout is driven by the tank’s operation on the battlefield. The tank must move across country at comparatively high speed, carry powerful armament, and protect the crew and the entire system. Tank configurations vary from year to year, but most countries have settled on a design that can be t r a d back to the The tank hull is normally divided into three compartments: the driver’s compartment, turret area, and the engine compartment. The engine of a tank is normally comparb mented to reduce the chance of a fuel fire spreading into the crew areas. The engine is normally found in the front or rear of the tank, but the first real tank, the British Mark I, had the engine in the middle.26 Although most tanks produced since WW 11 have the engine and transmission in the rear, many tanks were built before and during WW I1 with the engine in the rear and the transmission in the front.2’ There are several disadvantages to the rear engine/front transmission layout. T-34 tank The vehicle height must be increased to allow the driveshaft to transfer power to the transmission and, since a transmission requires maintenance, the front of a tank with a front-mounted transmission must have access hatches or removable armor to gain access to the transmission.28 Furthermore, front-mounted transmissions are vulnerable to mines because most mines detonate under the front of the vehicle. If this happens to a tank with a rear engine and transmission, an idler may be destroyed, but the tank can be short-tracked and moved away under its own power. On the other hand, if a front-mounted drive sprocket is hit, the tank cannot be moved and must be recovered by some other means. Yet another disadvantage of front-mounted transmissions is the necessity for mounting final drives close to the hull, thereby making it difficult to give the glacis plate a slope with a large angle from the vertical to provide the greatest possible effective thickness for the frontal amor.29 The only tanks in service today that have front-mounted engines and transmissions are the Israeli Merkava and the Swedish STank. The Merkava was designed with a front-mounted engine and transmission as additional frontal The STank’s front engine compartment also provides additional mew protection. However, ita front engine/transmission layout was really a byproduct of the requirement for an autoloader that filled the space where the engine would have been plad.31 As for maintenance of the S-Tank, if the 38 november-december 1983 b 1

SL","W".

Y w ", y,, " "w.w,"p,,,w,,, " I,, y, r L,,, y 1 - 1 1, "IW", y. - 7, I l" 11.11 "Y.., I "." 1.. 1 1 J, *. 201; Tank Warfare, p. 67. diesel engine must be replaced, not prjediles. (in) (mm) (mm) 13 54.5 1.384 37 'anther 65 1,650 75 14 69 1,753 75/76 1126 69 1,753 90 lger I 73 1,850 88 knturlon 74 1,880 83.4/105 148fM60 85 2,159 9011 05 Meftaln 85 2.159 120 n i i r n. narinn R na.,slnnrnan+ nf C;-h+in- I r a h i r l a r. n 74. UiinniPittt Dnmhinn. n only must the glacis plate be removed but the gun barrel must also be dismounM.32 With development of thermal imagers, front-mounted engines may increase the likelihood of the tank being detected in defilade, while the location of cooling radiators up front may also contribute to uneven main gun barrel heating and gun barrel droop. In addition to the disadvantages just mentioned, the problem of keeping the driver cool when he is located next to a hot engine or transmission is aggravated. However, keeping exhaust gases or noises out of the crew compartment is greatly simplified. A sigdicant advantage of locating the fighting compartment in the rear of the tank is the reduction of the overall length of the tank/hull/gun combination, which lowers the chances that the gun will strike the ground when moving across country with gun The rear fighting compartment configuration can also accommodate a longer gun, which increases muzzle velocity, and improves the penetration of armor-piercing, discarding-sabot (APDS) Most tanks mount the engine and transmission in the rear, avoiding the disadvantages of the h n t location, but this complicates the installation of controls because they must pass from the driver's compartment, through the turret area, and into the engineltransmission compart- m e r t. With the major exception of the S-Tank, most tanks have a single turret. The S-Tank has a fixed 105 mm gun mounted in the vehicle hull with an autoloader behind it that gives the system a 15round-per-minute rate of fire.36 Gun elevation of -10 to +12 degrees is obtained by using the hydropneumatic suspension to change the hull's pitch.37 The gun is traversed using a very sophisticated transmission to advance or reverse the tracks to change the gun's deflection. The system allows the gun to be traversed as rapidly as most tank turrets.38 Drawbacks to the S-Tank concept are rarely mentioned but obvious. The first is the total inability to fire the main gun on the move or from some positions. Since the entire hull must move to traverse the gun, an S- Tank commander cannot orient the gun while in turret defilade, order the driver to move forward, engage the target as soon as the gun is exposed, and then return to defilade.39 Although virtually all modern tanks have a single turret it is not impossible that in the future the crew will be positioned within the hull and the main gun mounted externally. The turret may be outmoded, but it offers advantages that no other system can match. If the commander is mounted above the hull, he has a better view of the terrain, is better able to spot targets and give s p d c instructions to the driver. Currently, the viewing systems necessary to do this are relatively simple, but mounting the commander and gunner in the hull would require complicated optical or electro-optical systems to ensure that vision would be at least as good as it is in a conventional turret. Armament The choice of a tank's main armament is governed by many factors. Among these are the tactical doctrine of the country developing the tank, the potential enemy's armor protection, and the requirement to destroy a variety of targets. In the 19608, it appeared that future tanks would be equipped with antitank guided missiles (ATGM) b e cause of their long-range and high kill probability. In the U. S., the Sheridan and M60A2 were designed primarily to fire ATGMs from their main gun. The French Army started to develop the ACRA, a 142-mm missile fired from a gun, but terminated the program after several fir- i n g. 3 Although missiles may have some advantages for long-range Roiled Homogeneous Armor 40.4 7.713 itanium 23.2 4.429 039 Aluminum 14.4 2.749 lotes: 1. Areal density is the weight per unit of surface area for a given thickness of material.

2. psf = Pounds per square foot of a one inch thick plate. engagements, their disadvantages include a low firing rate, inability to fire on the move, along minimum range, and reduction of the basic load because of their large size.44 In addition, because of their high cost, the crews of AGTM weapons systems fire very few training missiles. While the ATGMs were being developed, significant advances were made in tank gun fire control, permitting the gun to shoot more accurately at the ranges likely to be encountered in combat. Thus, all recently-fielded tanks mount guns as their main armament. Ammunition Tanks carry large volumes of ammunition for the main gun, coaxial machinegun, roof-mounted machinegun(s), the crew's weapons, 1 u uum.h nuuuuuuuu m a w u r a u u g and Tank Troops, p. 96.

november-december 1983 39

Year

Mark I (male) 332 57-mm 1916 Mark IV 204 57-mm 1916 1917 1918 1940 1941 1942 1944 1945 1945 1949 1-54 34 100-mm 1949 1950 1953 1953 1958

60 105-mm 5950 900 1960 T-62 40 11 5-mm 2000-3000 250 1967 Chieftain 64 120-mm 6Ooo 1963 Lempard 1 60 105-mm 5500 1965 1-64 40 125-mm 3Ooo 500 1970

33 152-mm 13 rnsl. 5560 1080 1974 T-72 40 125-mm 3000 50 1975 Leopard 2 42 120-mm 2000 1979 11,400 1000 1980 M1 -. -. 55 105-mm - - _-..............- wori Boa mal M 4 Sources: uuncan wow, APVS or woria war I: (uuncan Grow), American A t V S fd War 11, Ray Bonds, Modern Tanks and Fighting Vehicles, (Salamanc lk, Arc0 Publishing Inc), NY 1980, “Ordnance Tank Automotive Co id Characteristics Data, Tank, Combat, Full Tracked, 90-mm GI 8A2, ’* 22 Dec. 58. smoke grenades, and sometimes hand grenades. The most critical ammunition is that for the main gun. Historically, the number of main gun rounds aboard tanks has fluctuated greatly. For instance, the WW I Mark Itank, carried 332 57-mm rounds, and the WW 11, T-34/76 carried 77 main gun rounds (table 5). Since WW 11, the number of main gun rounds carried by main battle tanks (MBTs) has decreased in most countries. In the West, the consensus appears to be that 5@60 rounds are required, while the Soviets appear to accept about 40 rounds as the basic load. The weight and bulk of ammunition directly affects tank design and configuration. If more, or larger rounds, are to be carried, a penalty must be paid in equipment, crew space, or armor protection. Some examples: Increasing the basic load of an M-47 from 71 to 105 rounds required the removal of the bow machinegun and elimination of the bow gunner’s station.45 The 75mm round for the M-4 Sherman’s main gun weighs 20 pounds (9.04 kilos) and the tanks basic load weighs 1,931 pounds (875.88 kilos). By contrast, the M- 6OAl’s 105mm main gun round weighs 41 pounds (18.6 kilos) and its basic load weighs 2,460 pounds (1,116 kilos) (table 6). Empty cartridge cases add another problem for both the tank and ammunition designer. After firing as few as five rounds, the empty cases hinder the loader’s operations and the residual propellant gases held in the cases begin to pose a breathing problem for the crew.46 Some tanks have been designed with a port in the side of the turret for loading ammunition and disposing of spent cartridges, while ammunition for other tanks must be loaded through the loader’s hatch and empty cases thrown out through the same opening. The cartridge case disposal problem has been partially solved in tanks such as the T-64, T-72, and Leopard 2 by using combustible cartridge cases that leave only a relatively small obturator that resembles a very short cartridge case. The Chieftain is the only production tank using ammunition that does not have an obturator but has a completely combustible propellant bag instead. Crew The cubic volume of the tank devoted to the crew is a very important consideration in tank design. A seated man needs.52 cubic yards (0.4 cubic meters) of space when wearing nuclear-biological-chemical (NBC) gear. A loader needs 1.04 cubic yards (0.8 cubic meters), while the driver needs about.78 cubic yards (0.6 cubic meters). Allowing 10 percent extra for room and essential movement, a four-man crew requires about 3.3 cubic yards (2.5 cubic meters) of space.47 Many people wonder why tanks must have four-man crews. Modem electronics and engineering allow driving controls to be operated by either the commander or gunner. An automatic loader can replace a crewman, Indeed, the commander can, in most tanks, lay and fire the main gun. So why have more than one or two crewmen? us UK

UK us us UK us us us us

Sources: R. P. Hunnicutt, Sherman, A History of the American Medium Tank, (Tarus Enterprises), Belmont, CA. 1978, pp. 554567: Ezio Bonsignore, Anti-Tank Warfare, Technology, Trends, Weaponry (I), Military Technology 23, p. 31,

R. P. Hunnicutt, Pershing, (Feist Publications), Berkeley, CA 1971, pp. 23@ 231, Christopher F. Foss, Jane’s World Armored Fighting Vehicles, (Mac Donalds and Jane’s), London, 1976, pp. 94-95. 40 novernber-decernber 1983

T-64 203 Vlckera MBT 203 Leopard 1 (lat wheel) 260

'400 Leopard 2 530 S-Tank (last wheal) 543

550 - -,.... -...-..-..-. fense Review (IDR) Special Series: Main Battle Tanks (MBT), pp. 42-43; International Defense Review Special Series 11, Armored Vehicles, p. 22 "here is a E for a separat during an at mander finds shoots, and t the tank with by the comm cases, the dric and hand the! there is the indisputable fact that the fourth crew member reduces the strain on the crew by spreading out the workload of operating and maintaining the tank during 24-hour-a- day operations. However, the case for a separate loader is weaker. The Soviets have fielded two MBTs equipped with automatic loaders that offer a higher sustained rate of fire, but have the disadvantage of occupying as much space as a man. Furthermore, the automatic loader is subject to failure and requires maintenance to ensure reliability. The question of crew size will undoubtedly be raised again when new tanks are designed for the 1990s and the year 2000 since the watchwords will be smaller crews and greater mobility.48 Power Plant The power-to-weight ratio developed by the tank is widely regarded as the most critical measure of the tank's ability to move with some agility. Power-to-weight is normally expressed as the ratio of horse power-per-unit of vehicle weight and is found by dividing the gross power developed by the engine by the gross vehicle weight in tons. Power-to-weight ratios were in the 14-161 area during WW I1 and have risen to 27-28:l with the Leopard 2 and M1 tanks (table 8). These ratios provide rapid acceleration and sustained higher speeds that translate to improved agility and mobility, Centurlon 12.5 Chleftain 13.92 M-4A3 13.96 T-54 14.4

15.3 T-34/85 15.6 M48A5 15.9 1-55 16.1 1-44 16.2 M47 17.54 S-lank 18.7 T-72 19.0 1-62 19.2 Leopard 1A3 19.6 T-64 20.0 Leopard 2 27.5 M1 28.1 but the volume of the Leopard 2's diesel is only 5.19 cubic meters compared to the MI turbine's 5.48 cubic meters. However, most of the difference between the M1 and the Leopard 2 weight and space require menta for the propulsion systems of the M1 and thk Leonard 2 lies in the, - volume of fuel that must be carried aboard the MI -a problem that was solved by placing it in specially-shaped tanks to best use the available cia, Modern Armor, A Compre. hensive Guide, (Squadron/ Signal Publications), Warren, MI 1978, pp. 21-22, 25, 97, 106, 126 130.137.143.149. I,. -. - p a c e. Complicating the problem of com-Sumension paring different engine power ratings is the difference between gross horsepower (the power produced by an engine with no accessories) and the net horsepower (the power available to the transmission, after deducting cooling, electrical generating, and other losses). A case in point is the M48. Its AV-1790-5 gasoline engine developed 825 gross horsepower, while the diesel version developed 750 horsepower, but the diesel version produced 630 net horsepower compare to the gasoline engine's 625 net horsepower.51 Some observers are now beginning to believe that it is more important to quote the power-to-weight ratio at the sprocket rather than the gross power to weight ratio to account for these differences. The Soviets believe that the fao One of the a'ms of any euspen-sion system design is to produce a smooth ride by absorbing the shocks and jolts that occur when the tank maneuvers over varying terrain.53 Such forces are initially taken up by a springing medium consisting of either torsion bar, coil springs, Belle ville washers (disc springs), or hydropneumatic springs.54 In the hydropneumatic system, nitrogen gas in a sealed container is compressed when road wheel movement actuates a piston that forces oil against the gas. Then, as the road wheel clears the obstacle, the gas expands to move the wheel back to its normal position. Tanks without hydropneumatic suspension use shock absorbers to absorb the force that is not taken up by the springing medium. tors to be considered when picking a Regardless of what suspension is tank engine are the compactness used, the designer's primary objec-and reliability of the engine, its tive is to provide the smoothest ride accessability for maintenance, and possible. The smoother the ride, the novernber-decernber 1983 41

When considering the human factor in suspension design, it should be noted that motion sickness sets in when the hull’s pitching motion reaches 4 to 5 cycles per second.55 The desired goal is about.7 to.8 cycles per second, which can be achieved by increasing road wheel travel (table 7).56 Human Engineering Although the Soviets are frequent ly believed to ignore human engineering when designing tanks they do, in fact, consider the following factors closely: 0 Provision of comfortable head-rests. 0 Attention to layout of gunner’sand commander’s station for ease of operation. 0 Good depth of field for sights, thereby making them easier to use because placement of head is not as I Arthur J. Alexander, “Decision Making in Soviet Weapons Procurement,” Adelphia Papers, 147-148, (IISS), London, 1978, p. 31.

P. Aileen O’Brien “Generation of Weapons Requirements in the Soviet Ground Forces,” Army Research, Development and Acquisition Magazine, January-February 1980, p. 21.

A. Kh Babdzhanyan, ed., Tanks and Tank Troops (Red Banner of Labor Military Press of the Ministry of Defense of the USSR, Moscow), 1970, translated by the US Army Tank Automotive Command, Warren, MI, NTIS Number AD762 557, 1970 (hereafter cited as - fires). 0 Good ventilation. 0 Bore evacuators for quick removal of propellant gases from the gun tube.56 Also, the Soviets have included several design features not found in U. S. tanks that affect tank operation. On both the BMP and T-62 there are lights that warn the driver when the main gun is traversed over aline extended from the tracks forward. The vision blocks are electrically heated to demist them, and a spraying device is used to clear the vision blocks of mud or dust. On the T-62, the main gun cannot be power-traversed when the driver’s hatch is open. The BMP has alight to warn that the rear doors are open, and alight that tells the dnver that the gunner has applied power to the turret controls. Both Footnotes z2 Tanks and Tank Troops, pp. 103-104. 23 Design of Fighting Vehicles, p. 91. 24 Fred Schreier. “A Tank Designed to Cost -The US Army XM-1,” ZDR Special Series-11, 96 “Details of the Soviet T-72 Battle Tanks,” ZDR Special Series-11, p. 31. z6 Chris Ellis and Peter Chamberlain, ‘Tanks Mark I to V,” Duncan Crow, ed., AFV’s of World War One, (Profile Publications Limited, Windsor, Berkshire, England), 1970, p. 24. (hereafter cited as AFVs). 27 pp. 21-24. Tanks and Tank Troops. D. 51. Tanks and Tank Troops), p. 50.

F. Clifton Berry, Jr., “Solving the 144inch Mystery,” Armed Forces Journal Znternational, July 1970, p. 1820. Tanks and Tank Troops, p. 5859. Peter Chamberlain and Chris Ellis, “M-3 Medium (Lee Grant),”Armored Fighting Vehicles ofthe World. Volume 4. American AFV’s of World War ZZ(Profi1e Publications, Limited, Windsor, Berkshire, England), 1972, p. 48. R.

M. Ogorkiewin, Design and Development of Fighting Vehicles (Doubleday & Company, Inc., Garden City, NY), 1968 (hereafter cited as Design of Fighting Vehicles), p. 74. Tanks and Tank Troops, p. 96. Design of Fighting Vehicles. pp. 196-197. e Tanks and Tank Troops, p. 58. lo Design of Fighting Vehicles, pp. 7374. l1 Tanks and Tank Troops, p. 50. Tanks and Tank Troops, p. 4550. William Fowler, “Battle for the Falklands 0, Land Forces,” (Osprey Publishing, London), 1982, p. 19 Is Design of Fighting Vehicles, p. 96. Tanks and Tank Tmops, p. 96. Tanks and Tank Troops, pp. 94-96. “Zmproved Chieftain for Iran,” ZDR Special Series, Battle Tanks, 1976, pp. 96-97. la Design of Fighting Vehicles, p. 82. l9 Tank Warfare, pp. 111-113. MG I. Krupchenka “Characteristic Feature of the Development and Employment of Tank Troops,’’ Military History Journal, (Moscow), No. 9, 1979, pp. 2627. 21 Design of Fighting Vehicles, pp. 8283. z8 Tanks and Tank Troops, p. 56. 29 Tanks and Tank Troops, p. 51-52 30 “An Israeli Tank Ready for Series Production: The Merkava. Mk I,” International Defenee Review Special Series-11, Armored Vehicles. 1980, (Hereafter cited as ZDR Series- 11). pp. 3538. Main Battle Tanka, pp, 8890. 31 Main Battle Tanks, p. 90. 33 Tanks and Tank Troops, p. 57. a Main Battle Tanks. p. 87. Tanks and Tank Troops, pp. 5255. $0 Duncan Crow, Modern Battle Tanks, (Arc0 Publishing Company, NY), 1978, (hereafter cited as Modern Battle Tanks, p. 87. 37 Modern Battle Tanks, p. 83. 38 Modern Battle Tanks. p. 83-84. $9 Tank Warfare, pp. 145146. Footnotes 40, 41. and 42 are not shown because material that referred to them in the text was deleted. 43 Tanks and Tank Troops, p. 90. I4 Tanks and Tank Troops, p. 62. 46 AFVs of WWZZ, p. 229. 48 Tanks and Tank Troops. p. 87. 47 Tank Warfare, p. 135. (8 The discussion of crew size was based in large part on Simpkin’s Tank Warfare, p. 122- 125 and 127-133. The opinion on reasons for retention of the driver and loader are the author’s. ‘9 R. M. Ogorkiewin, “Gas Turbine or Diesels for Tanks,” ZDR Special Series 11, p. 85. 5O IDR Special Series - I I, p. 83. 51 Design of Fighting Vehicles, p. 89. the BMP and T-62 have marker lights to maintain formation while maneuvering at night. The lights facing forward are green, side lights are yellow or orange, and those in the rear are red. In addition, T-62 tanks have a removable hood with a vision block, windshield wiper, and electrical defroster that is placed over the driver’s hatch in bad weather.5’ Summary Tankers worldwide will probably always insist that the guy who designed his tank “blew” the design of one particular feature. While this may possibly by true, the tankers should be grateful if only one minor feature is faulty. Then, instead of griping among themselves, they should share their firsthand expe rience with equipment shortcomings through articles or letters to the editor of their professional journals. After all, who knows better about the quality of a tank than “the man who owns one?’ 52 s3 54 F. Schreier, “The Modern,,Battle Tank, Part 3 Mobility-3. Suspension, ZDR Special Series, Battle Tanks, 1976, (hereafter cited as Suspensions), p. 41. 55 Suspensions, pp. 41-42.,5e 57 “Tank Driver Hood,” Military Review 1972, p. 100 and “Modificantions to the T-62,” Armies & Weapons #35, June, 1977. Tanks and Tank Troops, p. 133. Tanks and Tank Troops, p. 135. Tanks and Tank Troops, pp. 8749. GERALD A. HALBERT graduated from California State University-Fullerton in 1974. He served with the 1Olst Airborne, 9th Infantry, 82d Airborne divisions, I Corps (ROW US) Group and XVlll Airborne Corps, 66th MI Group, and Hq. USAREUR. Prior to his retirement, he was assigned to Studies Division, Directorate of Combat Developments, USAARMS, Fort Knox. KY. 42 novernber-decernber 1983