Screw propulsion
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Screws can be used for vehicle propulsion. This works best over water, snow, sand, and other soft surfaces, although it can work as effectively over solid surfaces. This is normally done with pairs of screws: If they are rotated in opposite directions the vehicle will move forward; the same direction the vehicle will move sideways; different speeds cause the vehicle to turn. To date no production vehicles have been created using the screws. However, the Soviets with their first cosmonauts made vehicles that utilised such a drive to cross the tundra in Siberia since helicopter at that time were ill-equipped for the conditions. The British exploration team Ice Challenger also used the drive in their Snowbird 6 vehicle (a modified Bombardier tracked craft) to traverse the ice floes in the Bering Strait. In fiction, it is also the propulsion system for Metal Gear Solid 3's Shagohod.
