The Survivability of Tanks and Crews

This latest Soviet heavy tank was adopted and then deployed during the Winter War with Finland in 1940. Designated the KV-1, it was ordered into production in two variants. The first was the KV-1A, which was armed initially with a long-barrelled 76.2mm (3in) F32 main gun and 111 rounds of ammunition, substituted for the short-barrelled 76.2mm L-11 gun of early testing prototypes. The second model was the KV-2, a combination of the KV-1 hull, suspension and chassis with a huge turret mounting a 152mm (6in) howitzer.

During the course of World War II, no fewer than 11 variants of the original PzKpfw III production model, Ausf E, were built. Variants A to D were prototype models constructed in 1937 and 1938. With A to C the torsion-bar suspension was refined and with D and F, heavier armour, a higher-performance engine and an improved commander’s cupola were installed.

The interior of the PzKpfw III was spacious compared to other contemporary tanks, although space was diminished as larger main weapons were installed in succeeding variants. The driver was positioned forward and to the left in the hull, while a radio operator/machine-gunner was seated to the right. Three crewmen – the commander, gunner and loader – occupied the turret, which was centred on the hull. The 12-cylinder Maybach HL 120 TRM petrol engine developed 224 kilowatts (300hp) and was positioned at the rear. The torsion bar suspension had six road wheels with a frontal drive sprocket, rear idler and three return rollers.

There are four basic principles for ensuring the survival of a tank, known as crew-centric survivability, on the battlefield:

1. Avoid detection.
2. It the tank is detected, avoid being hit.
3. If the tank takes a hit, prevent penetration of the armour.
4. If the armour is penetrated, ensure survival of the crew and prevent the tank suffering fatal damage.

The first two principles relate to the tank’s active protection, and the latter two to its passive protection. We’ll take a look at them in order:

1. To remain undetected, it is necessary first of all to decrease the noticeability of the tank to a minimum as already discussed.
2. It is possible to avoid being hit by minimizing the area of the tank that is exposed to the enemy and the amount of time that the enemy can see it. This can be achieved:
3. a) by skilful use of the terrain and cover;
4. b) by artful manoeuvring so as not to expose the tank’s side, which presents a significantly larger area and, as a rule, weaker armour to enemy fire, than its front;
5. c) by maintaining a high speed on the battlefield; or
6. d) by decreasing the tank’s dimensions.

The tank’s technical features affect the last two points, primarily its power-to-weight ratio and the quality of the transmission and suspension, as well as its height, width and length. However, to a much larger degree everything depends on the crews themselves, their knowledge of combat tactics and their ability to master the handling of their combat vehicle. If decreasing the tank’s dimensions can lessen the probability of a hit on the tank by a matter of percentages, then the masterful exploitation of the terrain and cover combined with intelligent and rapid manoeuvring on the battlefield can reduce it by many times more.

3. Only a tank’s designed protection can prevent a shell that hits it from penetrating into its interior. (We have previously discussed the armour protection on the German and Soviet tanks.)
4. Even if the armour is penetrated by a shell, that still doesn’t necessarily mean the tank’s total demise.

We’ll discuss this in more detail. For a start, we’ll examine the main damaging factors of anti-tank ammunition. Primary among them in the period of our concern were the full-calibre, armour-piercing shells, the rear cavities of which were filled with small, but sufficiently powerful bursting charges. In addition to them, full-calibre solid armour-piercing shells – or so called solid shot shells – were also used. Armour-piercing shells penetrate armour due to their high kinetic energy. If it is sufficient, then as a rule, a shear plugging of the armour occurs, the diameter of which is approximately equal to the calibre of the shell itself. The after-penetration effect of an armour-piercing shell with a bursting charge depends on its remaining kinetic energy and the blast effect of its explosive. A solid shot has no blast effect, naturally, so its after-penetration effect is perceptibly lower than that of a shell with a bursting charge. However, it has greater kinetic energy, and accordingly better armour penetrating capability due to its larger inherent weight, because the specific density of an explosive charge is less than that of the metal of the shell’s body.

There are also other factors that enhance the potency of a shell’s effects. For example, often as a result of their penetration, so-called secondary fragments are often created within the tank. These are various pieces of the armour, parts and components that form as a result of their destruction, as well as unanchored objects. All this gets thrown around within the tank as a result of the influence of the shell’s kinetic energy and the armour plug punched out by it, as well as the blast effect of an armour-piercing shell with a bursting charge. The secondary fragments multiply and intensify the damage inside the tank, and also substantially increase the probability of injuring or killing the crew, so efforts are made to reduce their number to a minimum. Ideally, the result of the penetration of armour would be the appearance of one single plug that hasn’t been fragmented. However, in practice, fragments that have been chipped away or broken off from the armour surrounding the shell’s penetration frequently add to it. In order to prevent their creation, there are efforts to make the armour, especially its inner surface, as malleable as possible without sacrificing its resistance against shells. Other steps to decrease the severity of the consequences of the armour’s penetration include eliminating unsecured items within the tank and increasing the strength of both elements of the tank’s design and its parts and components, which when being destroyed turn into lethal secondary fragments. This is particularly important for the fighting compartment and driver’s compartment, where the tankers are positioned.

It is necessary to add that even when shells strike a tank yet fail to penetrate the armour, they sometimes nevertheless do damage to its crew and mechanisms. The main reason for this is the insufficient malleability of the interior surface of the tank’s armour, which as a result of the enormous stress caused by an impact that wasn’t able to penetrate the armour leads to spalling, the fragments of which are capable of not only damaging the tank, but also causing serious wounds and injuries to the tankers. This was typical of the T-34’s armour, especially of its cast turrets in the first half of the war. Heat treated for high hardness to its entire depth, it was prone to create secondary fragments. Remnants of moulding compound and burn-on from the casting process that haven’t been cleaned from the rear surface, surface defects of the rolled armour and dross from the welding seams are further sources of increased danger to the tankers. Blown free by the impact of a shell against the armour, they inflict painful wounds to a tanker’s exposed skin or the skin under their summer uniforms, and can even blind them.

As a result of the process of penetrating the armour and the conversion of the shell’s kinetic energy into heat during the process, the shell and the plug of armour (or its fragments, if it breaks into pieces) become heated to extremely high temperatures and acquire igniting capabilities. In the case of an armour-piercing explosive shell, the incandescent gases created during the explosion of the charge spread with extremely high velocity and pressure and add to their effect. Within any tank there are always items that are flammable. First and foremost there are the fuel and lubricants and the propellant charges of the stored ammunition, but there are also various rubber and plastic articles, paint, rags and the uniforms of the tankers, especially the winter uniforms. The very worst consequence of a fire in a tank is the detonation of the on-board ammunition and fuel storage, which results in the tank’s complete destruction. However, even without this, a burned-out tank becomes totally disabled and must be written off, since as a result of the lengthy effects of high temperatures during a strong fire, the tank armour loses its hardness and thus its protective qualities. In addition, because of the uneven heating of the burning tank, the hull and turret become irreversibly deformed, which is virtually impossible to correct. There is no sense in repairing such a tank, because it is much cheaper and faster to build a new one.

In the designs of their tanks the Germans took adequate measures in order to prevent fires. First of all, this included isolating the fuel tanks from the crew members. For example, the Pz.Kpfw.III’s fuel tank was in the engine compartment, separated from the fighting compartment by an internal firewall. Another such wall separated the fuel tank from the engine. On the Pz.Kpfw.IV the fuel tanks were located beneath the floor of the fighting compartment and were additionally protected by fireproof panels above them. Moreover, this section of the tank is usually shielded by folds in the ground when in combat and a direct hit on it is less likely.

In the Soviet tanks the situation with fire safety was much worse. For example, in the vehicles of the BT series, the fuel tanks were positioned between double walls in the area of the engine compartment and occupied a significant portion of the hull’s side profile. This created an unacceptably high likelihood that a shell hit would result in the ignition of at least one of them. In the T-34 that replaced them, the four fuel tanks (two upper with a capacity of 105 litres each and two lower with a capacity of 55 litres each) were placed right in the middle of the fighting compartment. Two more T-34 fuel tanks with a total volume of 145 litres were located in its transmission compartment. All three fuel tanks of the KV tank, with a total capacity of 600–615 litres, were also positioned along the sides of its fighting compartment.

The decision to place them in such an unsuitable place was taken as a result of the serious misjudgment of the combustion hazard of diesel fuel, although its flammability is significantly lower compared to petrol. The physics of this natural occurrence is rather simple. The fuel itself doesn’t burn, only its fumes do, thus the flammability of any fuel is characterized by two basic parameters:

1. The flash point: the lowest temperature of fuel at which its fumes create a mixture with the oxygen in the surrounding air, which combusts when it makes contact with an ignition source. Sustained burning in the process doesn’t yet arise because of the insufficient rate of fume production. On average, the flash point of various sorts of petrol is within the limits of –30 to –45º C., while that of diesel fuels is between 30º C. and 80º C.
2. The ignition point: the lowest temperature of fuel at which its fumes are produced at a sufficient rate to burn steadily after ignition from an external source. The ignition point of petrol is just 1–5º C higher than its flash point, while the analagous difference for diesel fuel is between 30 and 35º C.

Thus petrol easily ignites at a temperature above –25º C, while for diesel fuel the suitable conditions for ignition are created at much higher temperatures – at least 60º C., and for some types more than 115º C. These figures clearly explain why, when bringing a flaming torch close to an open container of petrol, it immediately ignites, but when rapidly plunging the same torch into a container of diesel fuel, the flame is extinguished. In the latter case, the torch simply doesn’t have time to heat up the diesel fuel to its flash point and dies when submerged in it because of the lack of oxygen necessary for burning. However, a hit by a shell or secondary fragments in a fuel tank filled with diesel fuel creates completely different conditions. Let’s analyse the main possible scenarios of this event:

1. When solid shot, shell fragments or pieces of armour strike a full fuel tank, they penetrate and create a fuel spillage. In the process, a fire rarely results because the solid shot, high-speed fragments and pieces which pass right through the penetrated fuel tank simply don’t have enough time to ignite the fuel over the very short time it takes to pass through it. In this case the fuel tank even serves as a supplementary defence against fragments and pieces that lack the energy to penetrate right through it. They also, as a rule, aren’t capable of igniting the fuel.
2. When an armour-piercing shell with a bursting charge strikes a full fuel tank and explodes either inside it or in direct proximity to it, the result is the total destruction of the fuel tank and the splashing of the fuel contained in it with its subsequent ignition.
3. When a solid shot, shell fragments or pieces of armour strike a fuel tank that is only partially full of fuel, they penetrate it. If the fuel tank is penetrated above the fuel level, but there are few fumes, then the solid shot, fragments or pieces pass completely through it and don’t cause a fire. If the penetration is below the fuel level, then the likelihood of fire depends on the correlation between the amount of fuel left in the tank and the amount of thermal energy transmitted to the fuel by the fragments or pieces. A small quantity of fuel in these conditions may ignite.
4. The most catastrophic consequences result when an armour-piercing shell with a bursting charge explodes in a fuel tank that is only 10–25 per cent full of fuel. In this instance an aerosol mixture of tiny drops of fuel and air forms, adding to the fuel fumes already within the fuel tank. The requirements for generating such a lethal cocktail are high temperature and abruptly increasing pressure created by the bursting charge’s blast effect. In order to trigger the mechanism of detonation of the mixture, this charge must be equivalent in power to not less than 50–100 grams of TNT, which at that time corresponded to an armour-piercing shell with a bursting charge with a calibre of 75mm and higher. The capacity of the fuel tank for creating the optimal conditions of mixing for detonation should amount to no less than 100 litres. In fuel tanks with a volume of 30–50 litres, there is no noticeable amplification of the shell’s blast effect. However, in the event that it happens, the detonation of the fuel tank increases the blast effect of the shell that explodes in it by two to four times. Thus, the explosion of a T-34 fuel tank, caused by the hit of a 76mm BP-350A armour-piercing shell, which contained 155 grams of TNT, was equivalent to the force of the explosion of a 152mm BP-540B armour-piercing shell with an explosive charge of 480 grams of TNT. As a result of a fuel tank’s explosion, the armour plate closest to its origin would be ripped from the hull along a welding seam and blown to one side. The tank’s turret, which usually gets blown off by detonation of the on-board ammunition, would remain in place in this event. Even the shells in the tank, despite the detonation taking place next to them, would often be left in their stowage racks. A conflagration virtually never resulted, and moreover, the fire that had already started would instantly die out. This is easily explainable: the powerful shock wave created by the fuel tank’s explosion extinguished the flame, and the available oxygen within the tank would instantly and completely burn out. A diesel fuel tank itself after a detonation inside it would disappear without a trace, having been blown apart into dust. Yet the explosion of an analogous fuel tank with petrol inside it was approximately 1.5 times weaker and wouldn’t cause the destruction of the tank hull’s welding seams. After the Germans introduced the use of shaped charge shells at the front at the end of 1941, cases of explosions of the T-34’s fuel tanks, which were filled only 25 per cent or less with fuel, began to be noticed from the effects of the explosive jet. However, only the diesel fumes contained in the fuel tank itself would detonate in this case. The resulting effects were equivalent to a charge of 30–50 grams of TNT, which would kill the entire crew, but the tank’s body would remain intact.

As is clear from the description of the dynamics of a fuel tank’s detonation and its consequences, all this fully corresponds to the process that occurs during the triggering of a contemporary fuel-air explosive, which is sometimes called a ‘vacuum bomb’. The speed of detonation approaches 1,500–1,800 metres per second, and the pressure up to 15–20 atmospheres. In the process, the mass velocity of the gas stream moving in the direction of the blast wave achieves 600–800 metres per second.6 It was this incredible force that tore apart the full strength penetration welded seams of the T-34’s hull. Tankers inside these tanks in such cases were killed instantly, with scarcely any time to sense anything.

Here it must be added that the Wehrmacht’s 37mm, 47mm and 50mm armour-piercing shells had insufficient explosive effect in order to cause the detonation of the T-34’s fuel tank. At the beginning of the war, really only the shells of the 88mm Flak 18/36/37 gun could trigger it, as could the 105mm K.18 cannon, which wasn’t encountered so frequently at the front line. However, the penetration of the T-34’s armour by guns with a calibre of up to 50mm also frequently had tragic consequences for their crews. A hit by a small calibre armour-piercing shell with a bursting charge on one of the fuel tanks in the fighting compartment, as a rule, meant the immediate ignition of the resulting spilled and spattered fuel directly among the tankers. In such circumstances, their chances of survival were very low. However, this isn’t all. The probability of the outbreak of a fire in the T-34’s fighting compartment also substantially increased as a consequence of the constant leakage of fuel from the fuel tanks positioned there. Most often the leak didn’t come from the tanks themselves, but from the rubber-canvas hoses and fittings that connected them. As a result, there were puddles of fuel on the floor of the fighting compartment, which easily ignited both from shells that penetrated the armour, as well as from the red-hot secondary fragments that resulted from the penetration. Moreover, ammunition boxes were stowed on the floor of the T-34’s fighting compartment, and the consequences of their ignition are not difficult to predict. However, this was not the worst scenario for the crews. The diesel fuel that seeped from the fuel tanks soaked into the tankers’ uniforms, which also became impregnated with fuel and lubricants during refuelling, repairs and maintenance, and when wiping the grease from shells while loading them aboard the tank, etc. Such cloth ignited very easily and it was virtually impossible to smother the flames. Burning diesel fuel caused much more serious burns to the men than did petrol. When petrol gets on the skin, first of all its fumes burn, so tankers who bailed out of burning tanks with petrol engines not infrequently got away with comparatively light burns. Blazing diesel fuel, unlike petrol, adheres tightly to the skin, burns much more slowly than petrol, and leaves deep burns on the body right up to the point of charring. It is no coincidence that special incendiary mixtures like napalm, which are intended to stick where they land, burn for a long time and at the same time reach a very high temperature, are made from heavy types of fuel, including diesel fuel.

A fire in the tank’s fighting compartment and driver’s compartment leads to an agonizing death for the men who aren’t able to bail out in time. The chances of saving the tankers’ lives increase if they have the ability to quickly abandon their burning vehicle. In the German tanks of the period under discussion, each crew member had his own hatch, so according to statistics, in the case of a tank catching fire, often the entire crew was able to get out, and in the worst case just two of the five crew members would not be able to escape. The German design engineers went so far as to weaken the sides of the turrets of their medium tanks by adding hatches to them, in order to give the crews a better chance in an urgent evacuation. However, the main point was that the Werhmacht’s tankers, in the majority of cases, had sufficient time to bail out of their tanks, because fires usually began in the engine compartment and didn’t always spread to the fighting compartment, and if they did, they didn’t do so immediately. For the T-34, the statistics were much worse. The fires in them often started in the fighting compartment because of the fuel tanks located there. From a burning tank, in the worst case no one managed to bail out, and in the best case, two might have been able to save themselves, usually the tank commander and driver-mechanic.

In the T-34 the driver-mechanic had the best chance of survival. In the first place, he was seated rather low and was partially screened from enemy shells by folds in the ground. Secondly, he was protected by a 45mm thick frontal hull plate, sloped at an angle of 60º from vertical, which was equivalent to 90mm of armour. The opening for the driver-mechanic’s hatch weakened the frontal armour, but on the other hand he was able to clamber quickly out of the tank through it. The radio operator and loader, however, had to wait for their turn to bail out, because they didn’t have their own hatches; wait, even when they were just seconds away from an agonizing death or a maiming injury from flames. The situation was no better with evacuation from the KV tanks, which had just two hatches for the five or six crew members. Moreover, the hatches sometimes became jammed because of the deformation of the hull or turret as a result of a shell’s hit. Therefore some tankers before a battle didn’t fasten the hatches, but instead lashed their covers with straps from within the tank into partially open positions. Hatches in this case loudly clapped when on the march and permitted shrapnel to enter the tank, but on the other hand the crew had a better chance to escape. Emergency escape hatches on the bottom of the vehicle appeared on Soviet tanks shortly before the war, and the BT-7M received them first. However, they weren’t suitable for an emergency abandonment of the tank. For example, in order to open the emergency hatch on the T-34, first six hex nuts had to be loosened, followed by the disengagement of six bolt bars, before the safety catch could be released, and only then could the hatch cover be dropped free. All this took on average 2.5 minutes, and around another minute was required for a trained crew of four men to exit through the emergency hatch. Hardly anyone could survive in a burning tank that long … Moreover, in the event of a fire in the tank’s work space, it was frequently impossible to use the emergency hatch – the burning diesel fuel spreading across the floor prevented this.

There is a widespread opinion that tanks equipped with petrol engines are much more flammable than tanks with diesel engines. As can be shown from the facts presented above, the fire hazard of combat vehicles to a much greater extent depends on their design and layout, rather than their engine type and fuel type. Therefore it is not appropriate to call, as often happens, all of the Soviet pre-war tanks that had petrol engines fire hazards. We have already looked at a case from the Winter War with Finland, when of the 482 cases of combat damage and mechanical failures of the T-28 tank, only 30 led to a fire that destroyed it. Such an impressive statistic convincingly demonstrates that the sensible positioning of the fuel tanks and the effective fire suppression system that equipped the T-28 successfully resulted in minimizing the number of cases of fatal outbreaks of fire in this tank after the penetration of its armour – despite its use of petrol as fuel.

Interestingly, the fire extinguishers on the Soviet tanks of that time were themselves dangerous for the tankers. The point is that they were filled with tetrachloride, which, under the effect of high temperatures, emits a suffocating gas – phosgene. So when using them inside a closed tank, it was required to don gas masks first.

The question is often discussed: why were the Wehrmacht’s tanks equipped with petrol engines? After all, the German engineers had ample experience with successfully designing various diesel engines, intended to equip automobiles, tractors, locomotives, ships and even aircraft. The point is that during the Second World War, there was an acute shortage of diesel fuel in Germany. Unlike petrol, the Germans were unable to synthesize it from coal, and they had plainly insufficient resources of natural oil available. The navy became the primary consumer of diesel fuel in the Third Reich. Many of its combat ships were equipped with diesel engines, including the so-called ‘pocket battleships.’ The German submarine force used an especially large number of diesel engines. It was in fact the deficit of diesel fuel that became the main reason for the use of petrol engines on the German panzers during the Second World War. There were also other reasons, however. For the ground forces, they filled not only tanks with petrol, but also prime movers, lorries, cars and motorcycles, which significantly simplified the system of the Wehrmacht’s supply with fuel. Moreover, a petrol engine has a number of considerable advantages over a diesel engine:

1. The same power is attainable with lower weight and size;
2. A larger operating range of rpms;
3. Superior acceleration;
4. Simplicity and low cost of production;
5. Ease of start at lower temperatures.

Its main shortcoming in comparison with diesel is its lower efficiency. Because of it, tanks equipped with petrol engines, as a rule, have a relatively short range between refills. However, back then, the Germans didn’t consider this a significant disadvantage.