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Tank

2007 Schools Wikipedia Selection. Related subjects: Military History and War

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

   A tank is a tracked armoured fighting vehicle, designed to engage enemy
   forces by the use of direct fire. A tank is equipped with heavy weapons
   and armour, as well as by a high degree of mobility that allows it to
   cross rough terrain at relatively high speeds. While tanks are
   expensive to operate and logistically demanding, they are among the
   most formidable and versatile weapons of the modern battlefield, both
   for their ability to engage other ground targets and their shock value
   against infantry. While tanks are powerful fighting machines, they
   seldom operate alone, being organised into armoured units in combined
   arms forces. Without such support, tanks, despite their armour and
   mobility, are vulnerable to infantry, mines, artillery, and air power.
   Tanks are also at a disadvantage in wooded terrain and urban
   environments, which cancel the advantages of the tank's long-range
   firepower, limit the crew's ability to detect potential threats, and
   can even limit the turret's ability to traverse.

   Tanks were first used in World War I to break the deadlock of the
   trenches, and they evolved gradually to assume the role of cavalry on
   the battlefield. The name tank first arose in British factories making
   the hulls of the first battle tanks: the workmen were given the
   impression they were constructing tracked water containers for the
   British Army, hence keeping the production of a fighting vehicle
   secret.

   During World War I two major types of tanks evolved; the "male tank"
   which is the vehicle associated with the word today, and the female
   tank. The female tank contained a series of smaller weapons located
   around the hull as opposed to the single large weapon seen on today's
   tanks, and was mainly designed as an anti-infantry platform. After
   World War I ended this type of vehicle was largely replaced by infantry
   carriers.

   Tanks and armour tactics have undergone many generations of evolution
   over nearly a century. Although weapons systems and armour continue to
   be developed, many nations have reconsidered the need for such heavy
   weaponry in a period characterised by unconventional warfare.

History

World War One: the first tanks

   The fighting conditions on the Western Front prompted the British Army
   to begin research into a self-propelled vehicle which could cross
   trenches, crush barbed wire, and would be impervious to fire from
   machine-guns. Having already seen a Rolls-Royce Armoured Car used by
   Royal Naval Air Service in 1914, and aware of schemes prompted by Major
   Ernest Swinton to create a tracked fighting vehicle, First Lord of the
   Admiralty Winston Churchill sponsored the Landships Committee to
   oversee development of this new weapon. The Landships Committee created
   the first successful prototype tank, nicknamed Little Willie, which was
   tested by the British Army in September 1915. Although initially termed
   landships by the Admiralty, the initial vehicles were colloquially
   referred to as water carriers, later shortened to tanks, to preserve
   secrecy. The word tank was used to give the workers the impression they
   were constructing tracked water containers for the British army in
   Mesopotamia, and the name 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), near Delville Wood on the 15 September 1916. The tank was
   commanded by Captain Harold Mortimore and whilst it assisted the
   British infantry to capture 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 16 April 1917. The first
   successful use of massed tanks in combat meanwhile occurred at the
   Battle of Cambrai on 20 November 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 armoured support. The tank
   would eventually make trench warfare obsolete.

   Initial results with tanks were mixed; significant reliability problems
   caused considerable attrition in combat. Deployment in small "penny
   packets" also lessened their nonetheless formidable tactical value and
   impact. The spear-thrust type application of the Blitzkrieg was only to
   be developed fully in WWII.

   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.

   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 24 April 1918 at Villers-Bretonneux, France,
   when three British Mark IVs met three German A7Vs.

   Demands from infantry to have tanks close by during attacks would have
   negative effects on British tank design and tactics well into World War
   II.
     * Tanks of WWI
          + Video clip of WWI tanks helping the Allies with an advance in
            Langres, France (1918).
     * .

Interwar years: advances in design and tactics

   Polish Vickers E.
   Enlarge
   Polish Vickers E.

   With the tank concept now established, several nations designed and
   built tanks between the two world wars. The British designs were the
   most advanced, due largely to their interest in an armoured 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. The US did little development
   during this period because the Cavalry branch was senior to the
   Armoured branch and managed to absorb most of the funding earmarked for
   tank development. Even George S. Patton, with tank experience during
   WWI, transferred from the Armoured branch back to the Cavalry branch
   during this period (because the US 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
   armoured and generally very slow. The overall idea was to use infantry
   tanks in close concert with infantry to effect a breakthrough, their
   heavy armour 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 fount 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 to practise, and it was their superior tactics, not superior
   weapons, that made 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 armour, 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-armouring
   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 Two

   World War II saw a series of advances in tank design. Germany, for
   example, initially fielded lightly armoured and armed tanks, such as
   the Panzer I, which had been intended for training use only. These
   fast-moving tanks and other armoured vehicles were a critical element
   of the Blitzkrieg. However, they fared poorly in direct combat with
   British tanks and suffered severely against the Soviet T-34, which was
   superior in armour, weaponry and cross-country performance while being
   equal in speed. By the end of the war all forces had dramatically
   increased their tanks' firepower and armour; 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
   tonnes. By the end of the war the standard German medium tank, the
   Panther, mounted a powerful, high-velocity 75mm gun and weighed
   forty-five tonnes.

   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. Tanks with
   limited suspension travel subject 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.

   By this time most tanks were equipped with radios (all U.S. and German,
   some Soviet; British radios were common, but often of indifferent
   quality), vastly improving the direction of units. 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 (armoured vehicles carrying large-calibre 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
   recognised as the most efficient siting of the main gun. In order to
   engage armoured 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
   Enlarge
   A Polish tank company equipped with T-54 tanks

   After WWII, tank development proceeded largely as it had before, with
   improvement to 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 armour 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 tank design after it. However, the Panther was not
   terribly well armoured, and could not really fight the heavy tanks on
   an equal basis.

   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 that tank's design principles,
   improving on its low profile, good armour, high mobility, and adding a
   100mm tank gun.

   Another new tank was the British Centurion tank. Centurion marks built
   in the late 1950s were able to resist hits from the infamous German 88
   mm gun, were armed with the deadly 105 mm Royal Ordnance L7, 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 antitank guided missiles (ATGMs), the
   focus in development shifted away from armour thickness, to armour
   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 continuous development of anti-tank weapons.

Design

   The three traditional factors determining a tank's effectiveness are
   its firepower, protection and mobility. Also significant is shock
   action, the psychological effect of a tank's imposing battlefield
   presence on enemy soldiers.

   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 maximise all three. For
   example, increasing protection by adding armour will increase weight
   and therefore decrease manoeuvrability; increasing firepower by using a
   larger gun will decrease both manoeuvrability and protection (due to
   decreased armour at the front of the turret).

Firepower

   A US Medium Tank M4A3E8 tank fires from a prepared position during the
   Korean war
   Enlarge
   A US 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
   armour-piercing and high-explosive ammunition, and machine guns for
   defence against infantry, light vehicles, and aircraft.

   The main weapon of any modern tank is a single large gun. Tank guns are
   among the largest-calibre weapons in use on land, with only a few
   artillery pieces being larger. Although the calibre has not changed
   substantially since the end of the Second World War, modern guns are
   technologically superior. The current common sizes are 120mm calibre
   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 (KE) penetrators 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 will affect long range accuracy.

   Usually, tanks carry other armament for short range defence against
   infantry or targets where the use of the main weapon would be
   ineffective or wasteful. Typically, this is a small calibre (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
   armoured vehicles. Additionally, many tanks carry a roof-mounted or
   commander's cupola machine gun for close-in ground or limited air
   defence. 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-armoured vehicles at close range.

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

Fire control

   Historically, tank weapons were aimed through simple optical sights and
   laid onto target by hand, with windage 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 industrialised countries
   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 systems to make them more accurate.
   Gyroscopes are used to stabilise 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 armour,
   including High explosive squash head (HESH, also called high explosive
   plastic, HEP), High explosive anti-tank (HEAT), and kinetic energy
   penetrators (KEP, or armour-piercing discarding sabot APDS). For
   accuracy, shells are spun by gun-barrel rifling, or fin-stabilised
   (APFSDS, HEAT-FS, etc.).

   Some tanks, including the M551 Sheridan, T-72, T-64, T-80, T-90, T-84,
   and PT-91 can fire ATGMs (anti-tank guided missile) 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 favour 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. Photo from B
   Company, 4th Tank Battalion, 4th Marine Division, US Marines.
   Enlarge
   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. Photo from B
   Company, 4th Tank Battalion, 4th Marine Division, US Marines.
   An M1 Abrams tank on lookout. Heat haze from the turbine engine can be
   seen to the rear.
   Enlarge
   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 armour
   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, however, once a tank starts its engine or begins
   to move it can be detected much more easily due to the heat 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 "randomise" or at least reduce the
   regularity of the thermal signature of a tank.

   Tanks are powered by a diesel or turbine engine of a power comparable
   to 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 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) ensure that they produce 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 War was that tanks like 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.

Armour

   Abandoning a disabled M-3 tank in training
   Enlarge
   Abandoning a disabled M-3 tank in training

   The main battle tank is the most heavily armoured vehicle in modern
   armies. Its armour is designed to protect the vehicle and crew against
   a wide variety of threats. Commonly, protection against kinetic energy
   penetrators fired by other tanks is considered the most important.
   Tanks are also vulnerable to antitank guided missiles; antitank mines,
   larger 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. The amount
   of armour 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 armoured fighting vehicles are manufactured of hardened steel
   plate, or in some cases aluminium. The relative effectiveness of armour
   is expressed by comparison to rolled homogeneous armour.

   Most armoured 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 armour is on the glacis plate and
   the turret front. The sides have less armour and the rear, belly and
   roof are least protected. Today, tanks are vulnerable to specialised
   top-attack missile weapons and air attack. 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
   armour-piercing ammunition, such as the Hurribomber's 40mm or Stuka's
   37mm, could be effective, also. Even a simple Molotov cocktail on the
   engine deck, however, may disable most tanks.

   Before the Second World War, several tank designers tried sloping the
   armour on experimental tanks. The most famous and successful example of
   this approach at the time was the T-34. Angling armour plates greatly
   increases their effectiveness against projectiles, by increasing the
   effective perpendicular thickness of the armour, 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.

   Even light infantry antitank weapons can immobilise a tank by damaging
   its suspension or track. Many tracked military vehicles have side
   skirts, protecting the suspension.

   High explosive anti-tank weapons (HEAT), 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 armour, steel mesh " RPG
   screens", or rubber skirts, were found to cause HEAT rounds to detonate
   too far from the main armour, greatly reducing their penetrating power.
   British Challenger 2 tank, fitted with Chobham Armour.
   Enlarge
   British Challenger 2 tank, fitted with Chobham Armour.

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

   Since the 1970s, some tanks have been protected by more complex
   composite armour, a sandwich of various 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 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 armour.

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

Passive defences

   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 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. 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 imagers 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 defences 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 millimetre and other very short wave
   radar.

Countermeasures

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

   Explosive reactive armour, or ERA, is another major type of protection
   against high explosive antitank weapons, in which sections of armour
   explode to dissipate the focused explosive force of a shaped charge
   warhead. Reactive armour is attached to the outside of an MBT in small,
   replaceable bricks.

   Active protection systems go one step further than reactive armour. An
   APS uses radar or other sensing technology to automatically react to
   incoming projectiles. When the system detects hostile fire, it
   calculates a firing resolution and directs an explosive-launched
   counter-projectile to intercept or disrupt the incoming fire a few
   metres from the target.

Exposed crew

   An Australian Sentinel tank during trials in 1942. Note the commander's
   lack of protection.
   Enlarge
   An Australian Sentinel tank during trials in 1942. Note the commander's
   lack of protection.

   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. In this rather high position, with no personal protection save
   maybe a helmet and a flak jacket, the commander can see around the
   vehicle with no restrictions, and has the greatest chance of spotting
   enemy antitank operations or natural and artificial obstacles which
   might immobilise or slow down the tank. Also, the tank itself is less
   visible as it can stay lower behind obstacles.

   Tank periscopes and other viewing devices give a sharply inferior field
   of vision and sense of the countryside. Thus, when a tank advances in
   hostile territory with hatches closed, the commander and the crew might
   be personally safer, but the tank as a whole is more at risk given the
   extremely reduced vision. In order to overcome this problem
   improvements in onboard optical systems are ongoing.

Mobility

   There are essentially three main aspects of mobility to consider, the
   tank's basic mobility such as its speed across terrain, the ability to
   climb obstacles and its overall battlefield mobility such as range,
   what bridges it can cross, and what transport vehicles can move it and
   turning. Mobility is what tankers and tank designers call 'agility'.
   Mobility of a tank is categorised as Battlefield Mobility, Tactical
   Mobility, or Strategic Mobility. The first is a function of its engine
   performance and capability of its running gear and is determined by
   aspects such as acceleration, speed, vertical obstacle capability and
   so on. The second is the ability of the tank to be readily transported
   within a theatre of operation. The third is its ability to be
   transported from one theatre of operation to other, dependent on its
   weight, air portability and so on.

   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 to 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 the road the fastest tank design is not much
   slower than the average wheeled fighting vehicle design. But in
   practice, the huge weight of the tank combined with the relative
   weakness of the track assembly makes the maximum road speed of a tank
   really a burst speed, which can be kept up for only a short time before
   there is a mechanical breakdown. Although the maximum off-road speed is
   lower, it cannot be kept up continuously for a day, given the variety
   and unpredictability of off-road terrain (with the possible exception
   of plains and sandy deserts).
   A Leclerc crossing a gap.
   Enlarge
   A Leclerc crossing a gap.

   Since an immobilised tank is an easy target for mortars, artillery, and
   the specialised tank hunting units of the enemy forces, speed is
   normally kept to a minimum, and every opportunity is used to move tanks
   on wheeled tank transporters and by railway 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 railway bridges and yards 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 roads riddled by 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 during combat. 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 antitank groups.

   Another mobility issue is getting the tank to the theatre 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.

   Some tank-like vehicles use wheels instead of tracks in order to
   increase road speed and decrease maintenance needs. These vehicles lack
   the superior off-road mobility of tracked vehicles, but are considered
   by United States planners as more suited for rapid reaction forces due
   to increased strategic mobility .

Water operations

   For most tanks water operations are limited to fording. The fording
   depth is usually limited by the height of the air intake of the engine,
   and to a lesser extent the driver's position. The typical fording depth
   for MBTs is 90 to 120 cm. (3-4 Feet.)

Deep fording

   A T-90, snorkel erected.
   Enlarge
   A T-90, snorkel erected.

   However, with preparation some tanks are able to ford considerably
   deeper waters. The West German Leopard I and Leopard II tanks can ford
   to a depth of several metres, when properly prepared and equipped with
   a snorkel. The Leopard snorkel is in fact a series of rings which can
   be stacked to create a long tube. This tube is then fitted to the crew
   commander's hatch and provides air and a possible escape route for the
   crew. The height of the tube is limited to around three meters.

   Some Russian/Soviet tanks are also able to perform deep fording
   operations, however unlike the Leopard, the Russian snorkel is only a
   few inches round and does not provide a crew escape path. Russian
   snorkels are also fixed in length, providing only a couple of metres of
   depth over the turret height.

   This type of fording requires careful preparation of the tank and the
   ingress and egress sites on the banks of the water obstacle. Tank crews
   usually have a negative reaction towards deep fording. This has
   influenced tactics in those countries where the psychological health of
   the crews or their capacity for rebellion is taken into account.
   However, if properly planned and executed this type of operation adds
   considerable scope for surprise and flexibility in water crossing
   operations.

Amphibious tanks

   Sherman DD (Duplex Drive) amphibious tank with waterproof float
   screens, in 1944. The float screen was raised in the water and rear
   propellers provided forward thrust.
   Enlarge
   Sherman DD (Duplex Drive) amphibious tank with waterproof float
   screens, in 1944. The float screen was raised in the water and rear
   propellers provided forward thrust.

   Some light tanks such as the PT-76 are amphibious, typically being
   propelled in the water by hydrojets or by their tracks.

   Often a fold down trim vane is erected to stop water washing over the
   bow of the tank and thus reducing the risk of the vehicle being swamped
   via the driver's hatch.

   In World War II the M4 Medium Tank "Sherman" was made amphibious with
   the addition of a rubberised canvas screen to provide additional
   buoyancy. It was propelled by propellers driven by the main engine.
   This was referred to as the Sherman DD (Duplex Drive) and was used on
   D-Day to provide close fire support on the beaches during the initial
   landings. The Sherman DD could not fire when afloat as the buoyancy
   screen was higher than the gun. A number of these DDs swamped and sank
   in the operation. This was due to rough weather in the English Channel
   (with some tanks having been launched too far out), and due to turning
   in the current to converge on a specific point on the battlefield,
   which allowed waves to breach over the screens. Those that did make it
   ashore, however, provided essential fire support in the first critical
   hours.

Power plants

   An M1 Abrams engine undergoing maintenance by the crew, with the turret
   turned sideways to expose the engine deck. Photo from B Company, 4th
   Tank Battalion, 4th Marine Division, US Marines.
   Enlarge
   An M1 Abrams engine undergoing maintenance by the crew, with the turret
   turned sideways to expose the engine deck. Photo from B Company, 4th
   Tank Battalion, 4th Marine Division, US Marines.

   The tank's power-plant supplies power for moving the tank and for other
   tank systems, such as rotating the turret or electrical power for a
   radio. Tanks fielded in WWI mostly used petrol (gasoline) engines as
   power-plants, unlike the American Holt Gas-Electric tank which was
   powered by a petrol (gasoline) engine and an electric engine. In the
   Second World War there was a mix of power-plant types used; a lot of
   tank engines were adapted aircraft engines. As the Cold War started,
   tanks had almost all switched over to using diesel, improved multi-fuel
   versions of which are still common. Starting in the late 1970s, turbine
   engines began to appear.

   The weight and type of power-plant (influenced by its transmission and
   drive train) largely determines how fast and mobile the tank is, but
   the terrain effectively limits the maximum speed of all tanks through
   the stress it puts on the suspension and the crew.

Multi-fuel diesels

   All modern non-turbine tanks use a diesel engine because diesel fuel is
   less flammable and more economical than petrol. Some Soviet tanks used
   the dark smoke of burning diesel as an advantage and could
   intentionally burn fuel in the exhaust to create smoke for cover. Fuel
   tanks are commonly placed at the rear of the tank, though in some
   designs, such as the Israeli Merkava, the diesel fuel tanks are placed
   around the crew area to provide an additional layer of "armour." Fuel
   has often been stored in auxiliary tanks externally, or by other means
   such as in a small trailer towed behind the tank, able to be detached
   during combat.

   Modern tank engines are in some cases multi-fuel engines, which can
   operate on diesel, petrol or similar fuels.

Gas turbines

   Gas turbine engines have been used as an auxiliary power unit (APU) in
   some tanks, and are the main power plant in the Soviet/Russian T-80 and
   U.S. M1 Abrams. They are comparatively lighter and smaller than diesel
   engines; at the same level of sustained power output (the T-80 was
   dubbed the Flying Tank for its high speed).

   However they are much less fuel efficient, especially at low RPMs,
   requiring larger fuel tanks to achieve the same combat range. Different
   models of the M1 Abrams have addressed this problem with battery packs
   or secondary generators to power the tank's systems while stationary,
   saving fuel by reducing the need to idle the main turbine. T-80 tanks
   are commonly seen with large external fuel tanks to extend their range.
   Russia has replaced T-80 production with the less powerful T-90 (based
   on the T-72), while Ukraine has developed the diesel-powered T-80UD and
   T-84 with nearly the power of the gas-turbine tank.

   Because of their lower efficiency, the thermal signature of a gas
   turbine is higher than a diesel engine at the same level of power
   output. On the other hand the acoustic signature of a tank with a
   muffled gas turbine can be quieter than a piston engine–powered one.
   The M1A2 was nicknamed Whispering Death for its quiet operation.

   A turbine is theoretically more reliable and easier to maintain than a
   piston-based engine, since it has a simpler construction with fewer
   moving parts. In practice, however, those parts experience a higher
   wear due to their higher working speeds. The turbine blades are also
   very sensitive to dust and fine sand, so that in desert operations
   special filters have to be carefully fitted and changed several times
   daily. An improperly fitted filter, or a single bullet or piece of
   shrapnel can render the filter useless, potentially damaging the
   engine. Piston engines also need well-maintained filters, but they are
   more resilient if the filter does fail.

   Like most modern diesel engines used in tanks, gas turbines are usually
   multi-fuel engines.

Command, control and communications

   Commanding and coordinating a tank organisation in the field has always
   been subject to particular problems. Because of the isolation of small
   units, individual vehicles, and even the crewmen of a tank, special
   arrangements have had to be made. Armoured bulkheads, engine noise,
   intervening terrain, dust, and smoke, and the need to operate "hatches
   down" (or "buttoned up") comprise severe detriments to communications.

Internal communications

   Every action of a tank's crew, movement and fire, is ordered by its
   commander. In some early tanks, the crew commander's task was severely
   hampered by having to load or fire the main armament, or both. In many
   small armoured fighting vehicles, even into the late twentieth century,
   the crew commander would relay movement orders to the driver by kicks
   to his shoulders and back. Most modern AFVs are equipped with an
   intercom, allowing all crew members to talk to each other, and to
   operate the radio equipment. Some tanks have even been equipped with an
   external intercom on the rear, to allow co-operating infantry to talk
   to the crew.

Tactical communications

   In the earliest tank operations, communications between the members of
   an armoured company were accomplished using hand signals or handheld
   semaphore flags, and in some situations, by crew members dismounting
   and walking to another tank. In World War One, situation reports were
   sent back to headquarters by releasing carrier pigeons through vision
   slits. Signal flares, smoke, movement, and weapons fire are all used by
   experienced crews to coordinate their tactics.

   From the 1930s to the '50s, most nations' armoured forces became
   equipped with radios, but visual signals are still used to reduce radio
   chatter. A modern tank is usually equipped with radio equipment
   allowing its crew to communicate on a company or battalion radio
   network, and possibly to monitor a higher-level network, to coordinate
   with other arms of service. Company or battalion commanders' tanks
   usually have an additional radio. Communications on a busy network are
   subject to a set of formalised language rules called radio voice
   procedure.

   Most armoured forces operate with the crew commander, and possibly
   other crew members, "hatches up", for best possible situational
   awareness. When taking fire, or in potential NBC conditions, tank crews
   "button up" and only view the battlefield through vision slits or
   periscopes, severely reducing their ability to acquire targets and
   perceive hazards. Since the 1960s, a tank's commander has had
   progressively more sophisticated equipment for target acquisition. In a
   main battle tank, the commander has his own panoramic sights (with
   night-vision equipment), allowing him to designate one or more new
   targets, while the gunner engages another. More advanced systems allow
   the commander to take control of the turret and fire the main armament
   in an emergency.

Computerised advances

   A recent development in AFV equipment is the increased integration of
   fire control, the laser range-finder, GPS data, and digital
   communications. U.S. tanks are fitted with digital computers which are
   connected into battlefield networks. These integrate known information
   on enemy targets and friendly units to greatly improve the tank
   commander's situational awareness. In addition to easing the reporting
   burden, these systems also allow for orders to be given complete with
   graphics and overlays, via the network.

   See also:
     * Military communications
     * Command, control, and communications (C3I)
     * C4ISTAR

Vulnerability

   Despite being a powerful weapon and an impressive sight on the
   battlefield, the tank is vulnerable. In fact, the tank's effectiveness
   has led to massive development of antitank weapons.

Infantry

   Despite a tank's long-range firepower and shock action against
   inexperienced infantry, unsupported tanks are vulnerable to attacks by
   foot soldiers when attacking defensive positions, in close terrain, and
   in built up areas. Tank weapons have blind spots below their minimum
   depression, and a tank's suspension and relatively thin rear and top
   armour are vulnerable to attacks from nearby and from the upper storeys
   of buildings.

   Tanks generally operate with closely coordinated infantry support to
   protect them from enemy infantry.

   Infantry antitank weapons include early petrol bombs and antitank
   rifles, antitank hand grenades, magnetic mines and sticky bombs, and
   various handheld shaped-charge weapons including bazookas, RPGs and
   antitank guided missiles (ATGM).

Artillery

   Since World War II, tanks are sufficiently armoured to protect against
   artillery shell fragments. Only massive barrages are likely to destroy
   tanks with lucky direct hits, or flip them over by near-misses with
   very heavy high-explosive shells. Artillery guns usually also have a
   few rounds of antitank ammunition for defence against tanks in direct
   fire.

   Since the 1970s, there have been several types of artillery ammunition
   developed which can attack armoured vehicles. These include guided
   projectiles which home in on a target painted by a laser designator.
   There are also cluster munitions, saturating an area with bomblets
   which can attack top armour or create a minefield, and even smart
   submunitions which can identify and attack nearby tanks.

Mines

   Antitank minefields are area-denial weapons, helping to defend an area
   which is covered by fire, or channel enemy movements to prepared kill
   zones. Undefended minefields or individual mines planted in roadways
   are also used to delay movement and act as a nuisance weapon, but are
   not considered a highly effective military weapon—although their effect
   on morale and public support for military missions is used by
   insurgents.

   Land mines attack a vehicle's relatively fragile suspension and thinner
   bottom armour, and many armoured vehicles are designed to reduce their
   effect. There are also off-route mines, which use a shaped-charge HEAT
   warhead to attack from the side. Guerilla fighters who don't have
   antitank mines at their disposal may build improvised explosive devices
   for harassment of armoured forces.

Aircraft

   Starting in the Second World War, ground attack aircraft have been able
   to destroy tanks using heavy machine guns, cannon, rockets, and guided
   missiles or guided bombs.

   Since the 1960s, another threat is the attack helicopter, exploiting
   high mobility and the use of terrain for protection, and carrying
   sophisticated fire-control equipment and heavy guided missiles. A
   helicopter is able to make a pop-up attack from behind cover, only
   exposing itself briefly.

Logistics

   Tanks have very high logistical requirements. They are very hungry for
   fuel, ammunition, maintenance, and replacement parts. Armoured forces
   cannot fight effectively if their requirements cannot be met due to
   shortages, poor planning, or enemy actions.

   They can also be disabled by the weather: starter batteries and
   lubricants fail in extreme cold, while engines and crew-members
   overheat in very hot weather.

Future research and development

   There has been much speculation as to how tanks will evolve for modern
   day conflicts. Current research involves making the tank invisible to
   radar by adapting stealth technologies originally designed for aircraft
   and a variety of luminosity and colour shaping technologies. Research
   is also ongoing in armour systems and new propulsion units.

   One clear trend is the increasing number of electrical and
   communication systems on a tank, such as thermal scopes and higher
   powered radios.

   If tank designs switched to electrical motors like some other heavy
   construction equipment, rather than a direct drive transmission, or
   used electromagnetic guns, as is being studied for ships, there would
   still be a need for a good power-plant. The turbine engine and diesel
   (or multi-fuel) power plants meet current power needs but it is also
   possible that other types of power-plants such as fuel cells will
   provide a viable option, and they have been experimented with. For
   example, a hybrid electric version of the M113 APC outperformed the
   conventional one in many areas, but only at the expense of smaller
   range. Reduction of signatures and multi-fuel capability give the
   Stirling engine an advantage, and it has been examined.

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