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Encyclopedia > Main battle tank
For other uses, see Tank (disambiguation).
The US M1A1 Abrams tank is a typical modern main battle tank. The turret is low-profile, well-integrated into the overall shape of the vehicle.

A tank is a tracked and armoured combat vehicle (armoured fighting vehicle), designed primarily to destroy enemy ground forces by direct fire. A modern main battle tank (MBT), designed predominantly for combat, is the most powerful direct-fire land-based weapon. It is distinguished from other armoured fighting vehicles primarily by its heavy armour and armament. It can cross rough terrain and move relatively quickly in short bursts, but is power-, maintenance-, and ammunition-hungry and is not designed for sustained operations.

Tanks were first used in World War I. The name "tank" first arose in British factories making the casings of the first battle tanks: the workmen were given the impression they were constructing tracked water containers for the British Army in Mesopotamia. Tanks have subsequently undergone many generations of design evolution and are now a fairly mature technology, but significant improvements continue to be made in tank subsystems. There is an ongoing arms race between tank armour and anti-tank munitions.



Full article: Tank history

The first prototype tank was tested for the British Army for the first time on September 6, 1915. Although termed "landships" by The Admiralty, to preserve secrecy the initial vehicles were referred to as "water-carriers" which was then shortened to "tanks"

The word "tank" was then used to give the workers the impression they were constructing tracked water containers for the British army in Mesopotamia. It was made the official name on December 24, 1915. Legend has it that after completion the tanks were shipped to France in large wooden crates. For secrecy and not to arouse any curiosity the crates and the tanks themselves were then each labeled with a destination in Russian for Petrograd. In fact the tanks were never shipped in crates: the inscription in Russian was applied on the hull for their transport from the factory to the first training centre at Thetford. This first tank, the Mark I, became operational at the Battle of the Somme on September 15, 1916. Parallel to the British the French developed the Schneider CA1, first used on April 16, 1917. The first successful use of massed tanks in combat occurred at the Battle of Cambrai on November 20, 1917.

Although the tank would eventually make the trench warfare of World War I obsolete, they were not a decisive factor in that war. Initial results with tanks were poor, with the tanks proving to be unreliable, underpowered, underarmoured, and incapable of navigating battlefield terrain. Nevertheless, the concept was seen to be sound, and allied tank designs improved during the war. Later tanks were more reliable, had more powerful engines, were capable of withstanding German armour-piercing bullets, and due to a rhomboid shape could navigate large obstacles. Germany also built a few tanks, but did not pursue the concept very far.

Between the two world wars, with the tank concept now established, several nations designed and built tanks. Many sizes of tank were considered, and a lot of development effort went into light tanks that would be useful primarily against infantry. However, with tank-versus-tank engagements now being a major consideration, it became clear that future tanks would need to be heavily armoured and carry large guns. Tank shape, previously guided purely by considerations of obstacle clearance, now became a trade-off, with a low profile desirable for stealth and stability.

Turrets, which had always been considered but were not previously a universal feature on tanks, were recognised as the way forward. It was appreciated that if the tank's gun was to be used to engage armoured targets then it needed to be as large and powerful as possible, making having one large gun with an all-round field of fire vital. Experiments with multiple-turreted vehicles (e.g. the Russian T-35) were quickly abandoned and the last tank design without a single turreted main gun was the American M3 Lee of early- and mid- World War II.

This German photograph from World War I shows a captured British tank. The foremost part of the tracks are high off the ground in order to climb obstacles. The main guns are side-mounted because the tall body and weight considerations make a turret impractical.

World War II saw the greatest rate of advances in tank design. Germany initially fielded lightly armoured and lightly armed tanks, such as the Panzer I which was originally intended for training use only. These fast-moving tanks and other armoured vehicles were a critical element of the German Blitzkrieg. Experimentation with tank sizes reached its logical conclusion during the war, with the rather impractical German 188-tonne Maus, of which only two were ever built and never saw combat, and the 1000-tonne Ratte, of which none were ever completed.

It was during this war that tanks were first equipped with radios, vastly improving their command and control. Tanks were also adapted to a wide range of military jobs, including mine clearance and engineering tasks. Some of these tank variants live on as other classes of armoured fighting vehicle, no longer called "tanks". All major combatant powers also developed tank destroyers and assault guns - motorized and usually armoured vehicles carrying tank guns but without turrets.

The role of tanks has evolved into a specific niche indicated by the modern term "main battle tank", and wide variations in size are no longer seen. Since World War II, tank design has gone through a series of refinements, rather than any radical changes. Guns have become larger, and targeting has improved to the point where a modern tank essentially never misses at typical engagement ranges. Armour has evolved from steel plate into composite armour, with refinements such as reactive armour, as anti-tank weaponry has evolved. Crew comfort is improved, and the use of video cameras has diminished the need for viewing ports through the armour.


The MBT is the most heavily armoured vehicle in modern armies. Its armour is designed to protect the vehicle and crew against all known threats, including kinetic energy penetrators fired from other tanks, anti-tank guided missiles (ATGMs) fired from infantry or aircraft, mines, bomb and artillery fragments and rocket propelled grenades (or similar). The amount of armour needed to protect against all these threats from all angles would be far too heavy to be practical, so when designing an MBT much effort goes into finding the right balance between protection and weight.

There are several different kinds of armour. The most common is called passive armour which comprises layers of battle steel, alloys and ceramics. One of the best types of passive armour is the British-developed Chobham armour, which is comprised of spaced ceramic blocks contained by a resin fabric matrix between layers of conventional armour. A form of Chobham armour is encased in depleted uranium on the massively protected M1A1 Abrams MBT.

Another major type of armour is reactive armour, which involves the armour "exploding" out towards the incoming round and diverting it. Reactive armour is most effective against shaped charge weapons while passive armour tends to be better against kinetic energy penetrators. Reactive armour tends to be attached to the outside of an MBT in small, replaceable units rather than being permanently incorporated into its main body. Secondary passive armour may also be attached to a tank, but this is not common.

Traditionally the thickness of the armour is very unevenly distributed. The thickest sections are usually on the front glacis plate and the front of the turret. The sides have much lighter armor and armour on the top of the turret is lighter still. The back of the tank, and the sections directly above the engine, in the rear, have the lightest protection of all. The tracks are only partly protected by steel skirts.

As a result of these design decisions, a tank group is relatively vulnerable to air attack and needs constant escort by anti-aircraft vehicles, when the enemy is at least partly in control of airspace. For the same reasons immobilized tanks are also very vulnerable to enemy artillery fire from anything from medium sized mortar to a large cannon. Unescorted tanks are also vulnerable to ambush by light infantry and guerrillas with hand held anti-tank weapons.

Paradoxically, a tank is usually in its safest state when the commander is in a personally unsafe position, riding in the open, head out of the turret, with no personal protection save his helmet and a flak jacket. In this rather high position the commander can see around the vehicle with no restrictions, and has the greatest chance of spotting enemy anti-tank operations or natural and unnatural obstacles which might incapacitate or slow down the tank. Tank periscopes and other viewing devices give a sharply inferior field of vision and sense of the countryside, despite constant advances in optics and electronics. Thus, when tanks advance in hostile territory with hatches closed, the commander and others might be personally safer but the tanks as a whole are more at risk, given the extremely reduced vision.

Armour research

In part to combat the threats of handheld anti-tank weapons, as well as to investigate ways of maintaining protection levels while reducing weight, the U.S. and U.K. are investigating a series of advanced armour technologies.

One technology under development is electro-magnetic armor. Used to defeat shaped charge warheads, the armor uses a massive magnetic charge to break apart and disperse shape charge jets. One proposed system uses a sensor net of fiber optics covering the vehicle. An impacting warhead will interrupt the flow of light through the fiber optics, registering a hit. An automated system registers the location and sends a signal to energize a powerful electric coil located behind the armor.

The spiraling electrons in the coil give rise to an intense magnetic field that interacts with the particles within the shape charge jet. Although shape charges generate enormous forces by travelling at up to 9 km/s, the stream maintains its penetrating power over a very short, and specific, distance. The magnetic field "pinches" the charge jet, making it unstable and dispersing its force so the warhead's penetration power is significantly degraded.

Using such a system could reduce main battle tanks from their current scale-tipping weight of 70 tons, down to a more manageable 20 tons, while providing superior protection. Such downsizing would also have strategic implications. Current U.S. heavy armor divisions can take months to move from the continental United States to locations around the world. A lighter MBT could make deployment faster.

Other technologies being considered for MBTs include active armor, similar to but different from reactive armor, which uses radar or other sensing technology to automatically react to incoming missiles. Once the system detects hostile fire, it caculates a firing resolution and deploys counter-projectiles to intercept and disrupt the incoming fire. Again the goal is to reduce overall tank armor while maintaining protection levels. (This system could present risks to friendly infantry operating in close proximity to tanks, as they do in urban battlefields.)


A US Sherman tank fires from a prepared position during the Korean war. In this mode it acts as an artillery piece.

The main weapon of any modern tank is its gun, the size of which is exceeded by only the largest howitzers. It is usually 120 mm calibre for western-built tanks and 125 mm for eastern-built. The gun fires kinetic energy (KE) penetrator rounds as well as high explosive (HE) ones. Some tanks have the ability to fire missiles through the main gun barrel, which gives it longer range and makes it useful against airborne targets. Usually, the vehicle has a machine gun coaxially mounted with the main gun. This machine gun is of relatively small calibre (7.62 mm - 12.7 mm) and used against soft targets such as infantry. However, a couple of French tanks such as the AMX-30 and AMX-40 carry a coaxial 20 mm cannon, which has a high rate of fire and can destroy lightly armored vehicles. Additionally, many tanks carry a roof-mounted machine gun for anti-aircraft fire.

Historically, tank weapons were unstabilised and aimed through simple sights, and were consequently only accurate at short range and only while the tank was stationary. Modern tanks have a variety of sophisticated systems to make them more accurate. Gyroscopes are used to stabilise the main weapon; laser range finders are used to calculate the range to the target; computers calculate the appropriate elevation and aim-point, taking into account wind speed, air temperature and other important factors. Night and infrared vision equipment is also commonly included. Laser target designators may also be used to pick out targets for guided munitions. Modern tanks can even fire reasonably accurately while moving.

Modern tanks, such as this Israeli Merkava Mk 4, can fire reasonably accurately while moving.

Most armoured vehicles carry smoke grenade launchers, which can rapidly deploy a smoke screen to visually shield a withdrawal from an enemy ambush or attack. The smoke screen is very rarely used offensively, since attacking through it blocks the attacker's vision and will give the enemy an early indication of impending attack. Modern smoke grenades work in the infrared as well as visual spectrum of light.

Some smoke grenades are designed to make a very dense cloud capable of blocking the laser beams of enemy target designators or range finders. In many MBTs, such as the Leclerc, the smoke grenade launchers are also meant to launch tear gas grenades and anti-personnel fragmentation grenades.

Whilst almost all tanks are armed with a cannon and one or two machine-guns, there is no reason that they can not carry other types of weapons. Some Israeli tanks contain small vertical mortar tubes which can be operated from within the tank, enhancing the anti-personnel capabilities and allowing it to engage targets which are behind obstacles. There have been proposals to equip other tank with dual-purpose smoke/fragmentation grenade launchers that can be reloaded form the interior. Some tanks have also had unusual main armaments which include flame-throwers and mortars.

Armour-piercing ammunition

There are several types of ammunition designed to defeat armour, including HESH (High Explosive Squash Head), HEAT (High Explosive Anti Tank), APDS/APFSDS (Armour-Piercing Fin-Stabilized Discarding Sabot, a type of kinetic energy penetrator).

HESH rounds require a rifled gun while HEAT and other rounds can use a smooth bore gun as well as a rifled one. The British army and the Indian army, convinced of the superiority of HESH rounds, are now the only ones to field main battle tanks with rifled guns.

HESH rounds contain a charge of plastic explosive that splatters on a small area of the enemy tank. The force of the impact and power of the charge exploding causes part of the interior armor to spall off and ricochet around inside, damaging equipment and killing the crew.


The caterpillar tracks of a tank (here an Israeli Merkava Mk-III) allow it to tackle most types of terrain, but they are only lightly armoured and are prone to mechanical failure.

A main battle tank is designed to be very mobile and able to tackle most types of terrain. Its wide tracks disperse the heavy weight of the vehicle over a large area, resulting in a specific ground pressure that might be lower than that of a man's foot. The types of terrain that do pose a problem are usually extremely soft ground such as swamps, or rocky terrain scattered with large boulders. In "normal" terrain, a tank can be expected to travel at about 30-50 km/h. The road speed may be up to 70 km/h.

The logistics of getting from point A to point B are not as simple as they appear. On paper, or during any test drive of a few hours, a single tank offers better off-road performance than any wheeled fighting vehicle. On a road the fastest tank design is not much slower than the average wheeled fighting vehicle design.

In practice, the huge weight of the tank combined with the relative weakness of the track assembly ensure that the maximum road speed of a tank is really a burst speed, which can be kept up for only a short time before there is a mechanical breakdown. The maximum off-road speed is much lower, but in general it cannot be kept up continuously for a day, given the variety of off-road terrains and their unpredictable nature, with the possible exception of plains and sandy deserts.

Since an immobilized tank is an easy target for mortars, artillery, and the specialized tank hunting units of the enemy forces, speed is normally kept to a minimum, and every opportunity is seized upon to move tanks on wheeled tank transporters and on railways instead of under their own power. Tanks invariably end up on railcars in any country with a rail infrastructure, because no army has enough wheeled transporters to carry all its tanks. Planning for railcar loading and unloading is crucial staff work, and rail bridges and railyards are prime targets for enemy forces wishing to slow a tank advance.

When moving in a country or region with no rail infrastructure and few good roads, or a place with good roads but mines or frequent ambushes, the average speed of advance of a tank unit in a day is comparable to that of a man on a horse or bicycle. Frequent halts must be planned for preventive maintenance and verifications in order to avoid breakdowns when the shooting starts. This is in addition to the tactical halts needed so that the infantry or the air units can scout ahead for the presence of enemy anti-tank groups.

Another mobility issue is getting the tank to the theater of operations. Tanks, especially main battle tanks, are extremely heavy, making it very difficult to airlift them. Using sea and ground transportation is slow, making tanks problematic for rapid reaction forces.

Power cells

Most tanks use a diesel engine because diesel fuel is very nonflammable even when exposed to a direct heat source. In many designs, such as the Israeli Merkava, diesel fuel tanks are placed around the crew area, effectively becoming the second layer of armor. A diesel engine is also very economical and offers better combat range than other engines. Drawbacks are that a diesel engine is hard to start because its fuel is stable and it lacks an instant burst of power. The dark plume and smell of exhaust are also problems and they make it harder for a stealthy approach. Some Russian tanks use this as an advantage and intentionally inject extra fuels to create a thick dark cloud of smoke for cover.

Some of the more recent tanks, like the latest iterations of the German Leopard MBT design, have multifuel internal combustion engines, which can operate on diesel, gasoline or other fuels. Certain designs, like the M1 Abrams from the United States, are powered by diesel/JP8 fueled turbines. The turbine powered engine sounds like a giant vacuum cleaner and is much quieter than an internal combustion diesel engine. However the exhaust is very hot and does not allow infantry to use the back of the tank as cover from enemy fire.

Gas turbines have proved popular in some recent tank designs. They offer "burst power" immediately and their efficiency is greater than that of other engines in many conditions. However, in their lowest speed of operation they still continue to consume fuel at a much higher rate than other types of engines. During the first Gulf War this was a severe handicap for the M1s since they needed to keep their turbines running even while stationary, burning huge amounts of fuel, in order to power their infrared imaging devices and other electronics, while diesel powered fighting vehicles around them could power their electronics at a much lower cost in fuel by having the engine run at low idling speed. This is why newer models of the M1 tank are fitted with an auxilliary power unit (APU), which is a much smaller turbine engine used for powering tank systems while stationary and is significantly more fuel efficient than the main engine is at idle.

In theory a turbine is easier to maintain than the traditional piston-based diesel or multi-fuel engine, since it has much fewer moving parts. In practice, the turbine blades move at extremely high speeds and are very sensitive to dust. In desert conditions, where fine sand and dust of all size gets in everywhere, special filters have to be fitted at the turbine air intake and they must be changed several times a day during operations. The filters must be fitted exactly with great care since even a small opening is enough to get sufficient dust inside to ruin the motor. A single bullet or a piece of shrapnel would render the filter useless.

Sonic, seismic and thermal traces

Non-moving tanks are very easy to camouflage, making detection, and hence annihilation from the air, difficult. However, once a tank starts its engine or begins to move, it can be detected in a number of ways.

Most tanks are powered by a diesel engine of a power comparable to a diesel locomotive. From the outside a tank smells, sounds, and feels quite like a diesel locomotive. The deep rumble of even a single tank can be heard a great distance on a quiet day, and the sharp diesel smell can be carried far downwind. When a tank stands still with engine running the land trembles around it. When moving, the vibrations are greater. The acoustic and seismic signatures of multifuel engines are comparable. The acoustic signature of a turbine engine is much greater: its high pitch whine can be much more easily distinguished from other sounds, near or far.

The very large output of a tank engine (typically in excess of 750 kW) ensures that it will always leave a distinct thermal signature. The unusually compact mass of metal of the tank hull dissipates heat in a fashion which marks it off sharply from other objects in the countryside. A moving tank is thus relatively easy to spot by good land-based or aerial infrared scanners. One of the reasons for the one-sided fighting during the Gulf Wars was that tanks like M1 Abrams had almost four times the nighttime infrared scanning range of T-72s used by the Iraqi army. Another factor in the Gulf War was that even when camouflaged and not moving, Iraqi tanks at night would cool at a different rate than their surroundings, making thermal detection easy.

Getting a tank to move proved to be important in the Kosovo conflict in 1999. During the initial few weeks of the conflict, NATO air sorties were rather ineffective in destroying Yugoslav tanks. This changed in the final week of the conflict, when the Kosovo Liberation Army began to engage tanks. Although the KLA had no chance of destroying the tanks, their purpose was to get the tanks to move whereupon they could be easily identified and destroyed by NATO air power.


See also

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