The_British_Army_in_North_Africa_1942_E15577

A tank transporter is a combination of a heavy

tractor unit A tractor unit (also known as a truck unit, power unit, prime mover, ten-wheeler, semi-tractor, tractor truck, semi-truck, tractor cab, truck cab, tractor rig, truck rig or big rig or simply a tractor, truck, semi or rig) is a characteristical ...

and a mating full trailer or

semi-trailer A semi-trailer is a trailer without a front axle. In the United States, the term is also used to refer to the combination of a truck and a semi-trailer; a tractor-trailer. A large proportion of a semi-trailer's weight is supported by a trac ...

(typically of the "lowboy" type), used for transporting

tank A tank is an armoured fighting vehicle intended as a primary offensive weapon in front-line ground combat. Tank designs are a balance of heavy firepower, strong armour, and good battlefield mobility provided by tracks and a powerful engi ...

s and other

armoured fighting vehicle An armoured fighting vehicle (AFV) is an armed combat vehicle protected by armour, generally combining operational mobility with offensive and defensive capabilities. AFVs can be wheeled or tracked. Examples of AFVs are tanks, armoured cars, ...

s. Some also function as tank recovery vehicles, the tractors of which may be armoured for protection in combat conditions. Used on roads, tank transporters reduce the

wear and tear Wear and tear is damage that naturally and inevitably occurs as a result of normal wear or aging. It is used in a legal context for such areas as warranty contracts from manufacturers, which usually stipulate that damage from ''wear and tear'' w ...

on tracks and the other components of the

powertrain A drivetrain (also frequently spelled as drive train or sometimes drive-train) is the group of components that deliver mechanical power from the prime mover to the driven components. In automotive engineering, the drivetrain is the components o ...

s of tracked vehicles. They also conserve fuel, are less damaging of road surfaces, and reduce tank crew fatigue. Overall, they are more efficient at moving tanks at higher speeds and longer distances than the tanks themselves.

Chassis designs

Three chassis designs have been used, generally in this order over time as loads became heavier, although there are exceptions.

Rigid chassis

The lighter tanks of

World War I World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, the United States, and the Ottoman Empire, with fightin ...

and the interwar period were carried on simple rigid flatbed

lorries A truck or lorry is a motor vehicle designed to transport cargo, carry specialized payloads, or perform other utilitarian work. Trucks vary greatly in size, power, and configuration, but the vast majority feature body-on-frame construction ...

Trailers

As the weight of tanks became too great for lorry chassis, separate trailers were developed. These carried the entire weight of the tank on their own wheels, putting no weight onto the tractor unit. They are pulled by a ballast tractor connected to a drawbar. The simplest trailer designs have only two axles, but heavier loads frequently require more than this. Multiple wheels per axle are common, usually four, sometimes eight. One advantage of ballast tractors is that they are capable of

double heading In railroad terminology, double heading indicates the use of two locomotives at the front of a train, each operated individually by its own crew. The practice of triple-heading involves the use of three locomotives. The practice of multi-headi ...

, where two tractor units are coupled to pull a particularly heavy trailer. Tank Recovery Unit T3 including Dart Truck Tractor T13 and Trailer T28

Other attempts have been made around 1942 with heavy-trucks as known for the Dart T13 Tank Tractor.

Steering

Some designs, such as the 1928 Aldershot design, Baxter, 1989, p.20 grouped pairs of axles at each end of the trailer. Others, such as the 70-ton Cranes trailer used to carry the Second World War-era Tortoise heavy assault tank had five axles, spaced along the length of the trailer. Baxter, Breakdown, p.50 The end-wheel designs have the advantages of better ability to cross rough ground and steering more easily. Those with axles throughout their length must have suspension that allows the axles to move and also allowing some steering. This makes them more complicated to manufacture. Placing the wheels at the ends also allows the chassis to dip down into a "well", giving a lower

centre of gravity In physics, the center of mass of a distribution of mass in space (sometimes referred to as the balance point) is the unique point where the weighted relative position of the distributed mass sums to zero. This is the point to which a force ma ...

during transport. The Cranes trailer had a frame split into two sections of two and three axles, with a carrying bed above them. The outermost four axles had Ackermann steering for their wheels. The German ''Sd.Ah.''116 trailer of World War II had a steersman's position on the rear bogie.

Semi-trailers

The ballast tractor for a drawbar trailer must be comparable in weight to its load if it is to have traction, which means that the total weight of the tractor-trailer combination might be as much as twice the useful load. By using a semi-trailer instead, some of the load's weight is instead carried by the tractor. This avoids the need to ballast the tractor, making a greater proportion of the total weight available for the load. Semi-trailers cannot be moved on their own, or pushed and pulled by ballast tractors. They are only mobile when connected to the correct tractor unit, which can limit their use in recovery. The simplest semi-trailer is "half of a trailer", having wheels at the rear only and an articulated connection to the tractor unit. A strong metal post or kingpin on the trailer fits into a socket or ' fifth wheel' on the tractor. Lowboy semi-trailers are commonly used to keep the load's center of mass low, as they have a low horizontal bed, with a gooseneck that rises up at the front to connect to the tractor unit. As with drawbar trailers, it is simplest if all the axles of a semi-trailer are concentrated at the rear, away from the tractor unit. However, heavier loads may require more axles, and steering gear may be needed at the front of the semi-trailer.

Loading

Ramps

The simplest means of loading the transporter is with a pair of hinged ramps at the rear. The load then drives up the ramps and onto the trailer under its own power. As tracked vehicles exist for their mobility across obstacles, they usually have no difficulty in doing this (however, see the "Power for loading" section below.)

Tilt beds

The Cranes trailer described above uses an entire see-saw tilting bed (and two small ramps). A manual hydraulic pump tilts the empty bed, bringing the loading end close to the ground. The tank drives up, then once past the see-saw fulcrum the bed tilts back under its weight.

Demountable axles

Some designs use a demountable axle, where the axle detaches from the bed of the trailer. Access to the load bed is now through low ramps, without needing to climb over the height of the wheels. Again, the intention is to keep centre of gravity low.

Power for loading

Although an operational vehicle can be driven on-board under its own power, this is a delicate operation, particularly with tracked vehicles, as their precise steering is limited. In particular, neutral steering, where one track goes forward and one backward causing the tank to turn on the spot, is likely to either damage the trailer bed or to cause the vehicle to fall off. A few transporters have been fitted with winches for loading, but this is uncommon. Baxter, 1989, p.71 More commonly a disabled vehicle is loaded with the assistance of a recovery tractor, either winching or pushing it on board.

Tank recovery vehicles

Some tank transports are equipped with

winch A winch is a mechanical device that is used to pull in (wind up) or let out (wind out) or otherwise adjust the tension of a rope or wire rope (also called "cable" or "wire cable"). In its simplest form, it consists of a spool (or drum) attach ...

es or cranes to also serve as tank recovery vehicles. Some are armoured recovery vehicles. Tanks are usually deployed in groups, with an equal number of transporters to support them. Recovery vehicles are more complex and more expensive and thus only a limited number are produced. For similar reasons, tank transporters are rarely armoured to recover tanks under fire, although tracked recovery vehicles frequently are. A rare few have been, such as the M26 "Dragon Wagon" of

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposing ...

Individual models

File:Diamond T M20.jpg, Diamond T M20 ballast tractor File:The British Army in North Africa 1942 E12293.jpg, Mack EXBX transporting a disguised Valentine tank in North Africa File:Floor FTF.jpg, FTF tank transporter tractor unit built by Floor Truck Factory in the Netherlands File:Floor FTF 4050 rear.jpg, The FTF tractor had a 475 hp Detroit two-stroke diesel engine with

Roots blower The Roots-type blower is a positive displacement lobe pump which operates by pumping a fluid with a pair of meshing lobes resembling a set of stretched gears. Fluid is trapped in pockets surrounding the lobes and carried from the intake si ...

File:Scammell-28Au8-6700.jpg, Scammell Contractor hauling Conqueror ARV2 FV222 tank recovery vehicle ( REME)