Tanks

A tank is a tracked armored fighting vehicle, designed primarily to engage enemy forces by

the use of direct fire. A tank is characterised by heavy weapons and armor, 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 the First World War 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.

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.

Design

The three traditional factors determining a tank's effectiveness are its firepower, mobility

and protection. The psychological effect on enemy soldiers of a tank's imposing battlefield

presence is called shock action.

Firepower is the ability of a tank to defeat a target. This takes into account the maximum

distance at which targets can be engaged, the ability to engage moving targets, the speed

with which multiple targets can be attacked, and the capability to defeat armoured vehicles

or entrenched infantry.

Mobility includes the speed and agility of driving cross-country, the types of terrain that

can be covered, the dimensions of obstacles, trenches, and water that can be crossed, the

ability to cross small bridges, and the distance that can be covered before refuelling is

required. "Strategic mobility" also includes the ability to travel at high speed on roads,

and the ability to be carried on rail or truck transport. Traditionally AFV mobility is

measured by the following metrics:

* engine power
* engine torque
* power-to-weight ratio
* road speed
* off-road speed (a somewhat nebulous figure given the possible variation)
* road range
* off-road range
* weight (bridge classification)
* ground pressure
* width of trench crossed
* vertical step climbed
* angle of slope that can be climbed
* angle of side slope that can be negotiated
* ground clearance
* unprepared fording depth
* prepared fording depth (if different)

Protection is the amount of armour, the type(s), how it is arranged (i.e., sloped or not),

and which areas are given more protection (e.g., the turret and tracks) and which receive

less (e.g., the rear of the chassis). It also includes low profile, low noise and thermal

signature, active countermeasures and other methods of avoiding enemy fire, and the ability

to continue fighting after damage has been sustained.

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).

How the compromise is achieved is influenced by a combination of factors, including military

strategies, budget, geography, political will, and the requirement to sell the tank to other

countries.

Examples of how different countries are influenced in their decisions are as follows:

* Britain has historically opted for better firepower and increased protection at the

expense of some manoeuvrability. Britain maintains a small, highly-trained professional

army, and so tank crew survivability is important. As limited resources may be available,

the crew needs to be able to maintain their tanks in the field.
* The USA has a large army with sophisticated weaponry and a complex array of mobile

support services. As their tanks are expected to rarely be away from support and repair

units, less emphasis is placed on the crew's ability to maintain the tank themselves or to

continue fighting with it once damage has been sustained.
* Soviet tanks are traditionally rugged, simple for production and maintenance

(characteristic of the Soviet-era idiom that "quantity has a quality of its own"), as

exemplified by the T-34. State-controlled design development proceeds in incremental

changes. Extensive maintenance is expected to be done in specialised depots. Tanks of this

class are opted to have the best combination of firepower, mobility, and protection.
* Israel is a small, but relatively rich, nation, with limited manpower in a hostile

political environment. Its primary concern is therefore crew survivability. To this end it

is the only nation to have produced a main battle tank with the engine placed at the front

and fuel surrounding the crew, to increase protection.



Weapons

Main article: tank gun
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 then 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 reticule. Range to the target was estimated

with the aid of a reticule (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. These were eventually replaced 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.
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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 antitank (HEAT),

and kinetic energy penetrators (KEP, or armour-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-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
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.


Armour

Main article: vehicle armour

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. World War II American M4 Medium tank crews found the

German Tigers to be practically invulnerable from the front, and were forced to employ flank

attacks. Today, tanks are vulnerable to specialised top-attack missile weapons and air

attack. During WW2, 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 antitank 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.

Some antitank 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

neutralizing 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.
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Grenade launchers, smoke and 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

antitank 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.
[edit]

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 focussed

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.