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Tank
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
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.
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.
Text is available
under the terms of the GNU Free Documentation License
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