Landship
A landship is a large vehicle that travels on land, as opposed to on water, air, or in space. Because of their large size, their use on land is seen as impractical due to terrain obstacles, and soft ground that cannot support such large weight. Such problems are non-existent on water and in space. However, vehicles similar to the concept of landships have appeared in various forms in the real world, and more commonly in works of fiction.
Compare with trams and trains, which are large segmented land vehicles (or groups of vehicles) that use rail tracks, road trains, which are large land vehicles that use roadways, articulated buses (another road vehicle type), amphibious vehicles, which can drive on land and on water, and hovercraft, which travel above the surface of both masses on an air cushion.
History
During World War I, the British proposed building "landships" - large (1000 tons or more) vehicles capable of crossing the trench systems of the Western Front, and the Landships Committee was formed to investigate these ideas for equipping the Naval Brigades. The impracticality of building such large vehicles and the needs of the British Army for more numerous smaller vehicles led to the much smaller first tanks. However, until after the Second World War, the British would continue to think of tanks in naval terms; e.g., the Cruiser tank operating like the ships of the same name. Quickly proving impractical were the battleship-equivalent heavy tanks, such as the multi-turreted Vickers A1E1 Independent and its assorted offspring. The Russian Tsar Tank, a super-heavy tricycle gun platform, was scrapped after a prototype proved difficult to maneuver and the vehicle was deemed vulnerable to ground fire.
A Super Heavy Tank and a Railway Gun, the Landkreuzer P. 1000 Ratte and Landkreuzer P. 1500 Monster, were the closest things ever to be designed that approaches the popular fictional conception of a landship. The Maus was the only super-heavy tank built by the Germans in WWII.
Bucket-wheel excavators are the biggest (externally powered) land vehicles ever built by man, but do not fit into the popular conception of a landship. The largest self-powered land vehicles are NASA's two crawler-transporters.
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— 555 tons fully loaded, armed with rockets, and carrying 500 marines or 3 tanks
The Mountbatten class hovercraft is the largest civilian hovercraft ever built, and is capable of traveling over relatively smooth land in addition to water. It is capable of carrying 418 people, and 60 cars. Hovercraft are also used by the military for their amphibious landing capabilities. They are commonly referred to as air-cushioned landing craft. These vehicles are usually very large compared to other land vehicles, and commonly carry other land vehicles like jeeps and armored vehicles.
Methods of propulsion
The main concern with moving such vehicles on land is torque, as their high mass presents a large amount of inertia to overcome. For this reason, the propulsion system must be able to supply considerable amounts of initial torque to get the machine moving from standstill.
If power supply is not a problem, electric motors may also be considered, as some types are able to produce maximum torque from zero revolutions per minute (rpm) and virtually maintain it all the way to redline. In comparison, internal combustion engines steadily build their torque as rpm increases until they hit a "torque peak", after which torque output begins to drop if engine speeds continue increasing.
Self-propelled
Self-powered "landships" are usually powered by internal combustion engines with horsepower levels measured in thousands. They either mechanically propel the machine through a drivetrain (like most tanks or the aforementioned unbuilt Landkreuzer P. 1000 Ratte), or ultimately end up running electric motors through intermediate generators, essentially being large electric vehicles (like the Terex 33-19 "Titan").
An example of the latter is the NASA crawler-transporter: the 16 traction motors have their own power supply, consisting of two 2,750 hp Alco diesel engines driving four 1 megawatt generators.
The type of solid physical contact maintained with the ground usually comes in the form of large continuous track or wheel arrays.
Externally powered
In this type, the main power supply is not on the vehicle itself. For instance, while the Bagger 288's mechanical drives are on board, the power needed to run them comes from an external source. Alternatively, a landship may be pushed or pulled by the land equivalent of a tugboat, or even run on sail power.
Fictional appearances
In fiction, a landship is a very large ship or vehicle designed for travel over land. They can be of various sizes, shapes, made of different materials and have different methods of propulsion. Fictional landships have appeared in books, comics and films.