Editing Tank (section)

===Mobility===
Another major aspect of the modern tank is mobility. While early WWI behemoths like the British Mark I and the German A7V were content to lumber slowly forward with all guns blazing at the enemy, the need for higher speed and better cross-country capacity soon became apparent. Mobility in general is dependent on four major components, namely: the tracks, the suspension, the transmission and steering mechanism and the engine itself. 

*Track design is as integral to the identity of a tank, as it allows it to move around without sinking into the ground. Modern tracks are so good at their job that a tank imparts a lower ground pressure (or weight per square inch on the surface) than an automobile tyre or a human foot. That said, they are a also a significant weak spot: they can break or slip off, leading to a complete loss of traction, and a stopped tank is a dead tank. Nowadays, tracks often use the so called "slack-track" approach: a number of road wheels low to the ground transfer the weight of the tank to the track, two sprocket wheels (one in front and one at the rear) transfer the motive energy to the track and a couple of return wheels on top keep the whole track tense while in use. (Other arrangements have been used historically, but they fell by the wayside due to either fragility, or being too maintenance-intensive.) Efforts are made to keep the height of the whole track assembly as low as possible, as no matter how cool the [[Wikipedia:Mark I tank|British Mark I]] looked, running the tracks over the top of the body is begging for a mobility kill. (Though to be fair to the Mark I, it needed its high tracks to cross trenches, and since it came first, there weren't really any weapons that could specifically take advantage of its exposed tracks at the time.)

*Even more than the tracks themselves, suspension is what allows tanks to travel easily over all terrain, absorbing all of the bumps and lumps. The earliest tanks did not have any suspension. By the Second World War however, you had vehicles using varying arrangement of helical and leaf springs to smooth the ride out a little. Most tanks now employ what is called torsion bar suspension, which translates the up-and-down movement of the roadwheel into a metal bar designed to resist twisting. A few newer models employ hydropneumatic suspension, which can be adjusted to cope with softer or harder terrain, as well as adding a few more degrees of elevation or depression for aiming the main gun.

*Transmission and steering of a tracked vehicle is quite complex in execution, however it is conceptually quite simple: turning is accomplished by accelerating one of the tracks and slowing/stopping the other one. While there have been many different combinations of engines/driveshafts/clutches/brakes to obtain this since the first WWI vehicles, modern tank design boils down to two concepts: Russian/Chinese ones favor two separate transmissions, one for each track; while Western ones prefer the so-called 'double differential' approach that adds a second driveshaft and idler sprocket wheel to each track that can be used to speed/slow it. One big advance of the modern tank (and tracked vehicle in general) is the so-called 'neutral steering' that allows the tracks to turn in opposite directions and the vehicle to easily and quickly turn on the spot, something a wheeled one would be hard-pressed to accomplish as quickly and smoothly (if at all).  

* As for the engines, most tanks designed prior to the Second World War but after the First World War utilized the same engines as trucks and buses (cheap but underpowered), while a few settled on downrated airplane engines (lots of power but unreliable). At the start of the war, only the Germans dedicated engine production for military vehicles (which led to problems that we won't get into here) but it was the Soviets who would later take the cake, with the relatively lightweight yet powerful diesel Model V-2 in the T-34 (seeing a pattern here?) that would go onto to power almost all of their tanks. Most tanks nowadays go for diesels but a few use turbines. A diesel has the advantage of being fuel-efficient but with a rather poor power-to-weight ratio, while turbines run on nearly anything flammable and have much better power-to-weight ratio and are quieter, but are ''very'' thirsty and their much hotter exhaust can present some trouble to camouflage the vehicle against IR sensors and hazard to accompanying infantry. In the interest of making warfare more environmentally friendly, we may eventually see tanks driven by electrical power and hydrogen-fuelled turbines.

By nature, tanks have some wading capability, capable of going through water that would stop your average automobile dead. To go through deeper waters usually requires extensive modifications. The first truly amphibious tanks for instance, required canvas screens to be attached for flotation, along with a propeller driven by the tank's own engine. Presently, a few tanks, most of them Russian, have the capability to be driven completely underwater, provided that they're provided with a snorkel.