Tank transporter



A tank transporter is a specialized road vehicle for the transport of tanks, to and from the battlefield or during peacetime. They are necessary to limit the mileage of the tracked vehicles (as the tracks have a limited lifetime) and also to reduce wear on road surfaces which can easily be damaged by such heavy vehicles. Tank transporters also use less fuel than tracked vehicles and may have a higher road speed if provided with a good road network.

They may also be used for wheeled armoured cars, or for unarmoured tracked vehicles, though the advantages of using transporters are usually less substantial in these cases.

Recovery vehicles
Transporters are merely for the carriage of tanks. It's not their function to recover a damaged, broken-down or bogged-down tank. Specialist armoured recovery vehicles are used for this, which may have powerful winches or even cranes. Tanks are usually deployed in groups, with groups of transporters to support them. Recovery vehicles are more complex and more expensive to build than transporters, so a handful of recovery vehicles need be supplied to support a troop of transporters.

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 "Dragon Wagon" of World War Two. In peacetime a main battle tank design will often be produced alongside a tracked armoured recovery vehicle based on the same chassis, so as to have a recovery vehicle available with adequate weight and power for that generation of tanks. In wartime it's more usual to recycle the previous generation of tanks as recovery tanks, so as to extend their useful life without using valuable production.

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 the inter-war period were carried on simple rigid flatbed lorries.

Trailers
As the weight of tanks became too much 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're capable of double-heading, where two tractor units are coupled to pull a particularly heavy trailer.

Steering
Some designs, such as the 1928 Aldershot design, grouped pairs of axles at each end of the trailer.

Others, such as the 70-ton Cranes trailer illustrated here beneath the Tortoise had five axles, spaced along the length of the trailer. 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 during transport. The Cranes' trailer had a frame split into two sections of two and three axles, with a further carrying bed above them. The outermost four axles had Ackermann steering for their wheels.

The German Sd.Ah.116 trailer of World War 2 (illustrated below.) went so far as to have steersman's position on the rear bogie, covered by the canvas tilt just visible in the background of the photograph.

Semi-trailers


The ballast tractor for a drawbar trailer must weigh comparably to its load if it's to have traction, which means that the total load might be as much as twice the useful payload. By using a semi-trailer instead, some of the load's weight is instead carried by the tractor. This avoids the need for ballasting it, making a greater proportion of the total weight available for the payload.

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.

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.

To keep the load's centre of gravity low, gooseneck trailers are used. These have a low horizontal loadbed, with a central spine that rises up at the front to connect to the fifth wheel.

As for drawbar trailers, it's simplest if all the axles of a semi-trailer are concentrated at the rear, away from the tractor unit. The sheer weight of some though requires more and more axles, and these may then need steering gear at the front.

Ramps
The simplest means of loading the transporter is with a pair of hinged ramps at the rear. The load then drives up and on under its own power. As tracked vehicles exist for their mobility across obstacles, they have no difficulty in doing this.

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


An operational vehicle can be driven on-board under its own power. This is a delicate operation, particularly with tracks, 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 loadbed or to cause the vehicle to fall off.

A few transporters have been fitted with winches for loading, but this is uncommon. More usually a disabled vehicle is loaded with the assistance of a recovery tractor, either winching or pushing it on board.