Machinists dreamed up the first screw-propelled vehicle in 1868. Since then other prototypes have popped up for use in war, in farming, in industry, and dare I say it? In our hearts.
The wheel is a very special invention, and it's gotten the world through some tough times, but it has its limitations. In deep snow, in slippery mud, or in water, it's useless. To get through those kinds of conditions, humanity needs another famous simple machine: the mighty screw. Although it didn't catch on as a mode of popular transportation, it existed for decades in areas where heavy-duty vehicles were needed.
Screw driven vehicles were great when it comes to tasks that need power. People who catered to industries like logging and farming, that require a lot of muscle, kept the concept alive in the early days. One tractor could haul two tons of lumber behind it. It's no surprise the vehicles were hardy. Screws are basically a variation on perhaps the earliest and most basic labor-saving machines; the inclined plane. Ask someone to lift a heavy object six feet into the air and set it on a platform, and for the most part they'll fail. Let them shove it, inch by inch up a ramp, and for the most part they'll succeed. The longer the ramp, the more gentle the slope, and the less effort they have to put into it. An inclined plane trades low effort over a long distance for high effort over short distance.
A screw is an inclined plane wrapped around a cylinder. If one of the threads of the screw wraps around it twice while traveling from the tip to the head, someone will have to turn the screw twice to make the screw travel forward one of its lengths. If the thread wraps around it six times, they'll have to turn it six times to travel forward one of its lengths, but they'll be able to use less force. Early screw driven vehicles made use of this trade-off to keep moving forward.
When the the 20th century came, and with it two world wars equipped with tanks, the vehicles got a lease on life - at least in theory. Because the threads of a screw work whether they're traveling lightly along the ground or embedded in mud or snow. They can make 360 degree turns by locking one side in place while turning the other, or if they're particularly well designed, turning the screw on one side one direction and the other side the other direction. Because the screws on such vehicles are huge, and because they don't necessarily have to be solid, the vehicles could even be aquatic. Filling both screws with air could make the tank - or car, or transport vehicle - bouyant enough to float in water.
Sadly, the screw driven vehicles just didn't have enough practical function and popular support to keep people interested once the wars ended. A few models lingered on, carrying out the concept's original function as farm equipment, but the wheel seems to have beaten them out.