Tank

: This article is about armoured fighting vehicles. For other meanings, see Tank (disambiguation).

Mobility

There are essentially two main aspects of mobility to consider, the tank's basic mobility such its speed across terrain and ability to climb obstacles, and its overall battlefield mobility such as range, what bridges it can cross, and what transport vehicles can move it. Essentially mobility of a tank is categorised as either 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.

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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.

Related Topics:
Terrain - Track - Swamp - Boulder - Road

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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.

Related Topics:
Off-road - Fighting vehicle

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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).

Related Topics:
Plain - Desert

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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 upon 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.

Related Topics:
Mortar - Artillery - Tank hunting - Tank transporter - Railway - Bridge

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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.

Related Topics:
Mine - Ambush - Horse - Bicycle - Preventive maintenance - Infantry

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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.

Related Topics:
Airlift - Rapid reaction force

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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 might be more suited for rapid reaction forces due to increased strategic mobility.

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Water operations

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. Typical fording depth for MBTs are 90 to 120 cm.

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Deep fording

However, with preparation some tanks are able to ford considerably deeper depths. 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.

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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.

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This type of fording requires careful preparation of the tank and the ingress and egress sites on the banks of the water obstacle.

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However if properly planned and executed this type of operation adds considerable scope for surprise and flexibility in water crossing operations.

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Amphibious tanks

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

Related Topics:
PT-76 - Amphibious - Hydro-jets

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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.

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In World War II the Sherman Medium tank 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 Sherman was referred to as the Sherman DD (Duplex Drive) and was used on D-Day to provide close and intimate 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.

Related Topics:
Sherman Medium tank - Sherman DD - D-Day

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A number of these DDs sank due to rough weather in the channel.

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Those that did make it ashore, however, provided essential fire support in the first critical hours, getting off the beaches.

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Power plants

The tank's power-plant supplies power for moving the tank and for other tank systems, such as rotating the turret or electrical power a radio. Tanks fielded in WWI all used petrol (gasoline) engines as power-plants. 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.

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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.

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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.

Related Topics:
Diesel engine - Diesel - Fuel - Israeli - Merkava

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Modern tank engines are in some cases multi-fuel engines, a form of two-stroke design which can operate on diesel, petrol or similar fuels. However the exhaust is hotter than a diesel giving a larger thermal signature (see below).

Related Topics:
Multi-fuel - Engine

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Gas turbines

Certain designs, like the Russian T-80 and the US M1 Abrams, are powered by gas turbines. Gas turbines have been used as an auxiliary power unit (APU) in other tanks but not as the main engine. They are comparatively lighter, offer higher amounts of sustained power output, and their efficiency is greater than that of other engines in some conditions. However, they are much less efficient at idle RPM. Newer models of the M1 have a secondary small turbine engine as an APU for powering tank systems while stationary, instead of idling the main turbine for this purpose.

Related Topics:
T-80 - M1 Abrams - Gas turbine - Auxiliary power unit

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In theory a turbine is easier to maintain than the piston-based engines, since there are much fewer moving parts. In practice, the turbine blades are very sensitive to dust. In desert conditions, where fine sand and dust gets in everywhere, special filters have to be carefully fitted and they must be changed several times a day during operations. An improperly fitted filter, or a single bullet or a piece of shrapnel could render the filter useless, potentially damaging the engine. Piston engines also need filters and these also need constant maintenance, but the engines are more resilient even if the filter does fail.

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