Tank

Some Definitions:

an artificial body of water, or a man-made reservoir, especially in India where the word originated, and sometimes in Britain,
a large container for liquid, hence also an aquarium (derived from the above meaning),
a terrarium or container for compressed gas (also derived from the above meaning),
to decline or crash as in a stock declining rapidly in price.

A tank is a tracked and armoured combat vehicle (armoured fighting vehicle, AFV), designed primarily to destroy enemy ground forces by direct fire. A modern main battle tank (MBT) is distinguished from other AFVs primarily by its heavy armour and armament.

Table of contents

1 History
2 Modern Tanks
3 Armour
4 Weapons
5 Mobility
6 Sonic, seismic and thermal traces
7 Armour piercing ammunition
8 Related articles

History

Winston Churchill was a keen advocate of the idea of an armoured vehicle to defeat enemy trenches. As First Lord of the Admiralty Churchill created a Landship Committee to develop the concept. Although Landship was a natural term coming from an Admiralty committee, it was considered too descriptive and could give away British intentions. The committee therefore looked for an appropriate code term for the vehicles. Water Container was considered but rejected because the committee would inevitably be known as the WC Committee. (WC is a common British term for a water closet or toilet.) The term tank, as in water tank, was finally accepted and the vehicles are known as such to this day.

The first prototype tank was tested for the British Army for the first time on September 6, 1915, and used in combat for the first time at the Battle of the Somme, 15 September 1916.

See Tank history

Modern Tanks

The MBT is the most powerful direct fire land based weapon. It is used mainly to combat other MBTs, but its weapons are effective against almost all targets. Although some MBTs can carry infantry, this is not its primary task.

The term MBT, or main battle tank is used to distinguish the most powerful and most modern type of tank in any army from lighter, less costly tanks which are sometimes used for airborne or amphibious operations, or from older tanks which are used in secondary roles.

Armour

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

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

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

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

Weapons

The main weapon of any modern tank is its gun, the size of which is exceeded by only the largest howitzers. It is usually 120mm calibre for western-built tanks and 125mm for eastern-built. The gun fires KE-penetrator rounds as well as High Explosive (HE) ones. Some tanks have the ability to fire missiles through the main gun barrel, which gives it longer range and makes it useful against airborne targets. Usually, the vehicle has a machine-gun coaxially mounted with the main gun. This machine-gun is of relatively small calibre (7.62mm - 12.7mm) and used against soft targets such as infantry. Additionally, many tanks carry a roof mounted machine-gun for anti-aircraft fire.

Many, if not most, MBTs carry smoke grenade launchers, which can rapidly deploy a smoke screen to visually shield a withdrawal from an enemy ambush or attack. The smoke screen is very rarely used offensively, since attacking through it blocks the attacker's vision and will give the enemy an early indication of impending attack. Modern smoke grenades work in the infrared as well as visual spectrum of light.

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

Mobility

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

The issue in getting from point A to point B is another important paradox in tank design. On paper, or during any "test drive" of a few hours a single tank offers better off-road performance than any wheeled fighting vehicle. On a road the fastest tank design is not much slower than the average wheeled fighting vehicle design.

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

Since an immobilized tank is an easy target for mortars, artillery and the usual specialized tank hunting units of the enemy forces, speed is normally kept to a minimum and every occasion is seized upon to move tanks on wheeled tank transporters and on railways, instead of on 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 rail embankment and dismount is crucial staff work, and rail bridges and railyards are prime targets for enemy forces wishing to slow a tank advance.

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

Sonic, seismic and thermal traces

Most tanks are powered by a diesel engine of a power comparable to a diesel locomotive. From the outside a tank smells, sounds, and feels quite like a diesel locomotive. The deep rumble of even a single tank can be heard a great distance on a quiet day, and the sharp diesel smell can be carried far downwind. When a tank stands still with engine running the land trembles around it. When moving on most grounds the vibrations are greater.

Some of the more recent tanks, like the latest iterations of the German Leopard MBT design, have multifuel internal combustion engines, which can operate on diesel or gasoline or other fuels. Certain designs, like the M1 Abrams from the United States, are powered by turbines, whose high pitched sound can be heard at a good distance.

The very large size (typically in excess of 1000 hp) of a tank's engine ensures that it will always leave a distinct thermal signature when operating in nature. 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 tank is thus relatively easy to spot by good land based or aerial infrared scanners.

Armour piercing ammunition

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

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