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Tank (military)

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Soldiers from 3rd Armored Cavalry Regiment provide cover for other troops with their M1 Abrams main battle tank in Biaj, Iraq.

A tank is an armored, tracked vehicle designed to engage enemies in warfare head-on, using direct fire from a large-caliber gun. Heavy armor and a high degree of mobility give it survivability, while the tracks allow it to cross rough as well as smooth terrain at high speeds.

First used in World War I to break the deadlock of the trenches, tanks and tactics for their use have undergone many generations of changes since then. They gradually assumed the role formerly performed by cavalry on the battlefield: to flank opposing positions with fast movement, or to penetrate defenses by massive concentration. Either movement may then be followed up by deep penetration into enemy rear areas, again supported by their high mobility. Tanks seldom operate alone, being organized into armored units, usually in combined arms forces. Without such support, tanks, despite their armor and mobility, are vulnerable to special anti-tank artillery, other tanks, anti-tank mines, infantry (at short ranges) as well as specialized anti-tank aircraft such as attack helicopters or close air support aircraft.

Although tanks are expensive to operate and support, they remain among the most formidable and versatile weapons on the modern battlefield, both for their ability to engage other ground targets (including fortifications) and their shock value against infantry. Yet, even as costly weapons systems and armor continue to be developed, many nations have reconsidered the need for such heavy weaponry in a period characterized by unconventional warfare.

History

World War I: the first tanks

Germans around a captured British Mark II tank. The front tracks rise high off the ground for climbing obstacles; the main guns are side-mounted to keep a low center of gravity.

The stalemate on the Western Front prompted the British Army to begin research into a self-propelled vehicle that could cross trenches, crush barbed wire, and be impervious to fire from machine guns. The First Lord of the Admiralty, Winston Churchill, sponsored the Landships Committee, which created the first successful prototype tank, "Little Willie" in September 1915.

Initially, in factories making the hulls of these battle tanks, workmen were given the impression they were constructing tracked water containers for the British Army, thereby keeping the production of a fighting vehicle secret. The vehicles were colloquially referred to as water carriers, later shortened to "tanks." The name "tank" became official in December 1915.

The first tank to engage in battle was D1, a Mark I British tank used during the Battle of Flers-Courcellette (part of the Battle of the Somme), on the September 15, 1916. Whilst it assisted the British infantry in capturing some German trenches, it was knocked out by friendly fire. The French developed the Schneider CA1 working from Holt caterpillar tractors, and first used it on the April 16, 1917. The first successful use of massed tanks in combat meanwhile occurred at the Battle of Cambrai on November 20, 1917. Tanks were also used to great effect in the Battle of Amiens, when Allied forces were able to break through entrenched German position due to armored support.

Germany fielded a small number of tanks during World War I, notably the A7V, of which only about twenty were produced. The first tank versus tank action took place on April 24, 1918, at Villers-Bretonneux, France, when three British Mark IVs met three German A7Vs. German forces initially lacked countermeasures, though they did (accidentally) discover solid anti-tank shot, and the use of wider trenches to limit the British tanks' mobility. However, changing battlefield conditions and continued unreliability forced Allied tanks to evolve throughout the war, producing models such as the very long Mark V, which could navigate large obstacles, especially wide trenches, more easily than their predecessors.

Initial results with tanks were mixed. Significant reliability problems caused considerable attrition in combat, with up to one third breaking down due to mechanical problems unrelated to enemy fire. Deployment in small "penny packets" also lessened their nonetheless formidable tactical value and impact. The spear-thrust type Blitzkrieg-tactics were fully developed only in WWII, and while the tank would eventually make trench warfare obsolete, World War I came to an end before this entirely came to pass.

During World War I, two major types of tanks were produced: the "male tank," which is the vehicle common in the world today; and the "female tank," which contained a series of smaller weapons located around the hull, as opposed to a single large gun. The female tank was designed mainly as an anti-infantry platform to defend the male tanks. After World War I ended, this type of vehicle was largely replaced by infantry carriers.

Interwar years: advances in design and tactics

Polish Vickers E.

With the tank concept now established, several nations designed and built tanks during the Inter-war period between the two world wars. The British designs were the most advanced, due largely to their interest in an armored force during the 1920s. France and Germany did not engage in much development during the early inter War years due to the state of their economy, and the Versailles Treaty, respectively (all German tanks had been destroyed as a condition of surrender). The United States did little development during this period because the Cavalry branch was senior to the Armored branch and managed to absorb most of the funding earmarked for tank development. Even George S. Patton, with tank experience during World War I, transferred from the Armored branch back to the Cavalry branch during this period (because the U.S. Army decided not to fund a tank corps).

Throughout this period, several classes of tanks were common, most of this development taking place in the United Kingdom. Light tanks, typically weighing ten tons or less, were used primarily for scouting and generally mounted a light gun that was useful only against other light tanks. The medium tanks, or cruiser tanks as they were known in the United Kingdom, were somewhat heavier and focused on long-range high-speed travel. Finally, the heavy or infantry tanks were heavily armored and generally very slow. The overall idea was to use infantry tanks in close concert with infantry to effect a breakthrough, their heavy armor allowing them to survive enemy anti-tank weapons. Once this combined force broke the enemy lines, groups of cruiser tanks would be sent through the gap, operating far behind the lines to attack supply lines and command units. This one-two punch was the basic combat philosophy of the British tank formations, and was adopted by the Germans as a major component of the blitzkrieg concept. J.F.C. Fuller's doctrine of WWI was the foundation for work by all the main pioneers: Hobart in Britain, Guderian in Germany, Chaffee in the U.S., de Gaulle in France, and Tukhachevsky in the USSR. All came to roughly the same conclusions, Tukhachevsky's integration of airborne pathfinders arguably the most sophisticated; only Germany would actually put the theory into practice, and it was their superior tactics, not superior weapons, that would make Blitzkrieg so formidable.

There was thought put into tank-against-tank combat, but the focus was on powerful anti-tank guns and similar weapons, including dedicated anti-tank vehicles. This achieved its fullest expression in the United States, where tanks were expected to avoid enemy armor, and let dedicated tank destroyer units deal with them. Britain took the same path, and both produced light tanks in the hope that with speed, they could avoid being hit, comparing tanks to ducks. In practice, these concepts proved dangerous. As the numbers of tanks on the battlefield increased, the chance of meetings grew to the point where all tanks had to be effective anti-tank vehicles as well. However, tanks designed to cope only with other tanks were relatively helpless against other threats, and were not well suited for the infantry support role. Vulnerability to tank and anti-tank fire led to a rapid up-armoring and up-gunning of almost all tank designs. Tank shape, previously guided purely by considerations of obstacle clearance, now became a trade-off, with a low profile desirable for stealth and stability.

World War II: Blitzkrieg and combined arms

World War II saw a series of advances in tank design. Germany, for example, initially fielded lightly armored and armed tanks, such as the Panzer I, which had been intended for training use only, and was inferior to, for example, French tanks in service at the same time. They fared poorly in direct combat with British tanks and suffered severely against Soviet T-34s, which were superior in armor, weaponry, and cross-country performance while being equal in speed. Nonetheless, these fast-moving tanks and other armored vehicles, competently used, proved a critical element of the Blitzkrieg.

By this time, most tanks were equipped with radios (all U.S. and German, some Soviet; British radios were common, but often of varying quality), vastly improving the direction of units. Earlier, tanks had been seen as infantry support weapons, and were forced to move at the pace of the infantry, but the new doctrines and command structures allowed them to be used on their own, or in cooperation with infantry, instead of in a "moving artillery" role. Closely associated requirements were to give infantry and logistics the speed to keep up with a rapid advance, thus creating mechanized infantry.

By the end of the war, all forces had dramatically increased their tanks' firepower and armor. For instance, the Panzer I had only two machine guns, and the Panzer IV, the "heaviest" early war German design, carried a low-velocity 75mm gun and weighed under twenty tons. By the end of the war, the standard German medium tank, the Panther, mounted a powerful, high-velocity 75mm gun and weighed forty-five metric tons.

Another major wartime advance was the introduction of radically improved suspension systems. The quality of the suspension is the primary determinant of a tank's cross-country performance, and tanks with limited suspension subjected their crew to massive shaking; this not only limits the speed at which the tank can travel, but also prevents firing while moving. Newer systems like the Christie or torsion bar suspension dramatically improved performance, allowing the late-war Panther to travel cross country at speeds that would have been difficult for earlier designs to reach on pavement.

Tank chassis were adapted to a wide range of military jobs, including mine-clearing and combat engineering tasks. All major combatant powers also developed specialised self-propelled guns: artillery, tank destroyers, and assault guns (armored vehicles carrying large-caliber guns). German and Soviet assault guns, simpler and cheaper than tanks, had the heaviest guns in any vehicles of the war, while American and British tank destroyers were scarcely distinguishable (except in doctrine) from tanks.

Turrets, which were not previously a universal feature on tanks, were recognized as the most efficient siting of the main gun. In order to engage armored targets the tank needed a single, powerful gun, unlike some prewar designs (like the Soviet T-35), which were often equipped with multiple turrets featuring low-calibre armament, or else mounted one larger gun in a fixed position. Most tanks retained at least one hull machine gun.

The Cold War and beyond

A Polish tank company equipped with T-54 tanks.

After WWII, tank development proceeded largely as it had before, with improvements in both the medium and heavy classes. Light tanks were now limited to the reconnaissance role, and in U.S. use, airborne support as well. However, the weight limitations of air transport made a practical light tank almost impossible to build, and this class gradually disappeared over time.

But the seeds for a true transformation had already been working their way into existing designs. A combination of better suspensions and greatly improved engines allowed late-war medium tanks to outperform early-war heavies. With only slightly more armor and somewhat larger engines to compensate, mediums were suddenly protected against almost all anti-tank weapons, even those mounted on heavy tanks, while at the same time having the mobility of a medium tank. Many consider the turning point to be the Panther, which became the inspiration for almost every Western post-war tank design-although the Panther was not quite up to the gun power and armor protection standards of the early cold war.

A highly successful post-war tank was the Soviet T-54, which started production in 1947. This successor to the T-34 of World War II represented a direct evolution of Russian tank design principles, improving on its low profile, good armor, high mobility, and adding a 100mm tank gun.

Another new tank was the British Centurion. Centurion marks built in the late 1950s, able to resist hits from the infamous German 88 mm gun, were ultimately armed with the deadly 105 mm Royal Ordnance L7 gun and could reach 56 km/h due to the excellent 650-hp Rolls-Royce Meteor engine. The Centurion replaced all British medium cruiser tanks and finally led to the demise of the heavy infantry tank class entirely, becoming what the British referred to as the "Universal Tank," soon to be known as the "main battle tank" in most forces, abbreviated MBT.

In response to the threat of anti-tank guided missiles (ATGMs), the focus in development shifted away from armor thickness, to armor technology. Gun technology remained remarkably similar even to WWI-era gun technology, with most tanks in service still being manually loaded, but with big advances in shell effectiveness.

Although the basic roles and traits of tanks were almost all developed by the end of WWI, the performance of twenty-first century counterparts had increased by an order of magnitude. They had been refined dramatically in response to continually changing threats and requirements, especially the threat of other tanks. The advancing capabilities of tanks have been balanced by developments of other tanks and by the continuous development of anti-tank weapons.

Design

The three traditional factors determining a tank's effectiveness are its firepower, protection, and mobility. Firepower is the ability of a tank to identify, engage, and destroy a target. Protection is the tank's ability to resist being detected, engaged, and disabled or destroyed by enemy fire. Mobility includes tactical mobility over diverse terrain on the battlefield, as well as strategic mobility the ability of the tank to be transported by road, rail, sea, and perhaps by air, to the battlefield.

Tank design is traditionally held to be a compromise between these three factors-it is not considered possible to maximize all three. For example, increasing protection by adding armor will result in an increase in weight and therefore decrease maneuverability; increasing firepower by using a larger gun will decrease both maneuverability and protection (due to decreased armor at the front of the turret). These three factors are discussed in detail below. In addition, there is the psychological factor: the shock effect created by the imposing presence of tanks on a battlefield.

Firepower

A U.S. Medium Tank M4A3E8 tank fires from a prepared position during the Korean war.

The crew of a tank must be able to quickly identify, engage, and destroy many types of targets on the battlefield, while maintaining high mobility. To this end, they are equipped with sophisticated detection and fire-control equipment, a large gun capable of firing armor-piercing and high-explosive ammunition, and machine guns for defense against infantry, light vehicles, and aircraft.

The main weapon of any modern tank is a single large gun. Tank guns are among the largest-caliber weapons in use on land, with only a few artillery pieces being larger. Although the caliber has not changed substantially since the end of the Second World War, modern guns are technologically superior. The current common sizes are 120mm caliber for Western tanks and 125mm for Eastern (Soviet and Chinese legacy) tanks. Tank guns have been able to fire many types of rounds, but their current use is commonly limited to kinetic energy penetrator (KEP) and high explosive (HE) rounds. Some tanks can fire missiles through the gun. Smoothbore (rather than rifled) guns are the dominant type of gun today. The British Army and the Indian Army are now the only ones to field main battle tanks carrying rifled guns.

Modern tank guns are generally fitted with thermal jackets which reduce the effect of uneven temperature on the barrel. For instance, if it were to rain on a tank barrel the top would cool faster than the bottom, or a breeze on the left might cause the left side to cool faster than the right. This uneven cooling will cause the barrel to bend slightly and affect long range accuracy.

Usually, tanks carry other armament for short range defense against infantry or targets where the use of the main weapon would be ineffective or wasteful. Typically, this is a small caliber (7.62 to 12.7 mm) machine gun mounted coaxially with the main gun. However, a couple of French tanks such as the AMX-30 and AMX-40 carry a coaxial 20mm cannon that has a high rate of fire and can destroy lightly armored vehicles. Additionally, many tanks carry a roof-mounted or commander's cupola machine gun for close-in ground or limited air defense. The 12.7-mm and 14.5-mm machine guns commonly carried on U.S. and Russian tanks and the French Leclerc are also capable of destroying lightly-armored vehicles at close range.

Some tanks have been adapted to specialized roles and have had unusual main armament such as flame-throwers. These specialized weapons are now usually mounted on the chassis of an armored personnel carrier.

Fire control

Historically, tank weapons were aimed through simple optical sights and laid onto target by hand, with wind speed estimated or assisted with a reticle. Range to the target was estimated with the aid of a reticle (markings in the gun sight which are aligned to frame an object of known size, in this case a tank). Consequently, accuracy was limited at long range and concurrent movement and accurate shooting were largely impossible. Over time these sights were replaced with stereoscopic range-finders, and later by laser range-finders.

Most modern main battle tanks in the armies of industrialized nations use laser range-finders but optical and reticule range-finders are still in use in older and less sophisticated vehicles. Modern tanks have a variety of sophisticated fire-control systems to make them more accurate. Gyroscopes are used to stabilize the main weapon; computers calculate the appropriate elevation and aim-point, taking input from sensors for wind speed, air temperature, humidity, the gun-barrel temperature, warping and wear, the speed of the target (calculated by taking at least two sightings of the target with the range-finder), and the movement of the tank. Infrared, light-amplification, or thermal night vision equipment is also commonly incorporated. Laser target designators may also be used to illuminate targets for guided munitions. As a result modern tanks can fire reasonably accurately while moving.

Ammunition

There are several types of ammunition designed to defeat armor, including High explosive squash head (HESH, also called high explosive plastic, HEP), High explosive anti-tank (HEAT), KEP, and armor-piercing discarding sabot (APDS). For accuracy, shells are spun by gun-barrel rifling, or fin-stabilized (APFSDS, HEAT-FS, etc.).

Some tanks, including the M551 Sheridan, T-72, T-64, T-80, T-84, T-90, T-96, and PT-91 can fire ATGMs through their gun barrel or from externally mounted launchers. This functionality can extend the effective combat range of the tank beyond the range afforded by conventional shells, depending on the capabilities of the ATGM system. It also provides the tank with a useful weapon against slow, low-flying airborne targets like helicopters. The United States has abandoned this concept, phasing the M551 and M60A2 out of their forces in favor of helicopters and aircraft for long range anti-tank roles, but CIS countries continue to employ gun-missile systems in their main battle tanks.

Protection

Sections of the side-skirt are swung aside on this M1 Abrams tank to expose the track so that a road wheel can be replaced.An M1 Abrams tank on lookout. Heat haze from the turbine engine can be seen to the rear.

A tank's protection is the combination of its ability to avoid detection, to avoid being hit by enemy fire, the ability of its armor to resist the effects of enemy fire, and its ability to sustain damage and complete its mission, or at least protect its crew.

Avoiding detection

Stationary tanks can be well camouflaged in woodland and forested areas where there is natural cover, making detection and attack from the air more difficult. By contrast, in the open it is very hard to hide a tank. In both cases, once a tank starts its engine or begins to move it can be detected much more easily due to the heat signature and noise generated by its engine. The tank tracks across lands can be spotted from the air, and in the desert movement can stir up dust clouds several times the size of the tanks.

A recently stopped stationary tank has a considerable heat signature. Indeed even if the tank itself is hidden, for example behind a hill, it is still possible for a skilled operator to detect the tank from the column of warmer air above the tank. This risk can be reduced somewhat by the use of thermal blankets which reduce the radiation of heat while the engine and tracks cool. Some camouflage nets are manufactured from unevenly distributed mix of materials with differing thermal properties, which are designed to randomize or at least reduce the regularity of the thermal signature of a tank.

Tanks are powered by a diesel or turbine engine capable of powering a diesel locomotive. From the outside a diesel powered tank smells, sounds, and feels quite like a diesel locomotive. The deep rumble of even a single tank can be heard for 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 multi-fuel engines are comparable. The acoustic signature of a turbine engine is much greater: its high-pitched whine can be much more easily distinguished from other sounds, near or far.

The very large power output of modern tank engines (typically in excess of 750 kW or 1,000 hp) ensures that they produce a distinct thermal signature. The unusually compact mass of metal of the tank hull dissipates heat in a fashion which contrasts sharply with 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 War was that tanks like the M1 Abrams had almost four times the night-time 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 from their surroundings, making thermal detection easier.

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 Serbian tanks. This changed in the final week of the conflict, when the Kosovo Liberation Army began to engage tanks. Although the KLA had little chance of destroying the tanks, their purpose was to get the tanks to move whereupon they could be more easily identified and destroyed by NATO air power.

Armor

Abandoning a disabled M-3 tank in training.

The main battle tank is the most heavily armored vehicle in modern armies. Its armor is designed to protect the vehicle and crew against a wide variety of threats. Commonly, protection against KEPs fired by other tanks is considered the most important. Tanks are also vulnerable to ATGMs, antitank mines, large bombs, and direct artillery hits, which can disable or destroy them. Tanks are especially vulnerable to airborne threats. Most modern MBTs do offer near complete protection from artillery fragmentation and lighter antitank weapons such as rocket propelled grenades (RPGs). The amount of armor needed to protect against all conceivable 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.

Most armored fighting vehicles are manufactured of hardened steel plate, or in some cases aluminum. The relative effectiveness of armor is expressed by comparison to rolled homogeneous armor.

Most armored vehicles are best-protected at the front, and their crews always try to keep them pointed toward the likeliest direction of the enemy. The thickest and best-sloped armor is on the glacis plate and the turret front. The sides have less armor, while the rear, belly, and roof are least protected.

Before the Second World War, several tank designers tried sloping the armor on experimental tanks. The most famous and successful example of this approach at the time was the T-34. Angling armor plates greatly increases their effectiveness against projectiles, by increasing the effective perpendicular thickness of the armor, and by increasing the chance of deflection. German tank crews were said to be horrified to find that shots fired at the angled plates of T-34s would sometimes simply ricochet.

During World War II, aircraft rockets earned a formidable reputation, especially in France after the Normandy landings (Operation Neptune); post-war analysis revealed many reported kills were near-misses. Aircraft cannon firing armor-piercing ammunition, such as the Hurribomber's 40mm or Stuka's 37mm, could also be effective.

Today, tanks are vulnerable to specialized top-attack missile weapons and air attack, as well as specialized mines. Even light infantry antitank weapons, however can immobilize a tank by damaging its suspension or track. Many tracked military vehicles have side skirts, intended to protect the suspension.

HEAT weapons, such as the bazooka, were a new threat in the Second World War. These weapons carry a warhead with a shaped charge, which focuses the force of an explosion into a narrow penetrating stream. Thin plates of spaced armor, steel mesh "RPG screens," or rubber skirts, were found to cause HEAT rounds to detonate too far from the main armor, greatly reducing their penetrating power.

British Challenger 2 tank, fitted with Chobham Armor.

Some anti-tank ammunition (HESH or HEP) uses flexible explosive material, which squashes against a vehicle's armor, and causes dangerous spalling of material inside the tank when the charge explodes. This may kill the crew without penetrating the armor, still neutralizing the tank. As a defense, some vehicles have a layer of anti-spall material lining their insides.

Since the 1970s, some tanks have been protected by more complex composite armor, a sandwich of various alloys and ceramics. One of the best types of passive armor is the British-developed Chobham armor, which is comprised of spaced ceramic blocks contained by a resin-fabric matrix between layers of conventional armor. A form of Chobham armor is encased in depleted uranium on the very well-protected M1A1 Abrams MBT.

The Israeli Merkava tank takes the design of protection systems to an extreme, using the engine and fuel tanks as secondary armor.

When the armor is defeated then the ability of the surviving crew to escape becomes an issue. The provision of escape hatches, for instance the in bottom of the hull as in the T-34, or the side, as in the Churchill, are necessary potential weaknesses in the armor.

Passive defenses

Most armored 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 gives the enemy an early indication of impending attack. Modern smoke grenades work in the infrared as well as visible 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 and of course obscuring vision, reducing probability of a hit from visually aimed weapons, especially low speed weapons, such as anti-tank missiles which require the operator to keep the tank in sight for a relatively long period of time. In many MBTs, such as the French-built Leclerc, the smoke grenade launchers are also meant to launch tear gas grenades and anti-personnel fragmentation grenades. Many 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. This idea first appeared in German tanks during WWII and there have been proposals to equip other tanks with dual-purpose smoke/fragmentation grenade launchers that can be reloaded from the interior.

Prior to the widespread introduction of thermal imaging the most common smoke grenade in AFV launchers was white phosphorus which created a very rapid smoke screen as well as having a very useful incendiary effect against any infantry in the burst area (e.g., infantry attempting to close with hand placed charges or mines).

Since the advent of thermal imaging most tanks carry a smoke grenade that contains a plastic or rubber compound whose tiny burning fragments provide better obscurant qualities against thermal imagers.

Some tanks also have smoke generators which can generate smoke continuously, rather than the instantaneous, but short duration of smoke grenades. Generally smoke generators work by injecting fuel into the exhaust, which partially burns the fuel, but leaves sufficient unburned or partially burned particles to create a dense smoke screen.

Modern tanks are increasingly being fitted with passive defensive systems such as laser warning devices, which activate an alarm if the tank is "painted" by a laser range-finder or designator.

Other passive defenses include radio warning devices, which provide warning if the tank is targeted by radar systems that are commonly used to guide antitank weapons such as millimeter and other very short wave radar.

Countermeasures

Passive countermeasures, like the Russian Shtora system, attempt to jam the guidance systems of incoming missiles.

Explosive reactive armor, or ERA, is another major type of protection against HEAT weapons, in which sections of armor explode to dissipate the focused exp

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