A hovercraft or air cushion vehicle floats on a layer of compressed air just above the ground. It is also called a ground-effect machine. The air means there is very little friction between the craft and the ground.
A hovercraft has one or more big fans that suck air into the craft, then blow it down underneath. The air is trapped underneath by a flexible rubber skirt.
The idea began with Sir John Thornycroft in the 1870s. He thought the drag on a ship’s hull could be reduced if an indent allowed it to ride on a cushion of air. But no-one could work out how to contain the air.
In the 1950s Christopher Cockerell cracked the problem by pumping air down around the edge of a curtain-like skirt. The air itself then sealed the cushion of air inside the curtain.
In 1959 the world’s first practical hovercraft, the SRN 1, was built using Cockerell’s system. It crossed the English Channel on the 50th anniversary of Bleriot’s first flight across the Channel.
In the late 1960s the US army and navy began using hovercraft in the Vietnam War for patrol and rescue missions because of their ability to go over land, water and swampy ground equally easily. The Russian and US armies are still the biggest users of hovercraft.
In 1968 big hovercraft able to carry scores of cars and lorries were introduced as ferries across the English Channel, but elsewhere they have not lived up to expectations. The biggest cross-Channel hovercraft was the 56 m-long SRN4 Mk! 1 1 which carried 418 passengers and 60 cars.
In the late 1950s French engineer Jean Berlin developed a train called a tracked air cushion vehicle. This is basically a hovercraft on rails. Trains like this could swish between cities almost silently at speeds of 500 km/h.
On 25 January 1980 a 100 tonne US Navy hovercraft, the SES 100-B, reached a record speed of 170 km/h – faster than any warship has ever travelled.