An "ekranoplan" literally "screen plane" is a vehicle resembling an aircraft, but operating solely on the principle of ground effect. Ground effect vehicles (GEV) fly above any flat surface, with the height above ground dependent upon the size of the vehicle.
During the Cold War, ekranoplans were sighted for years on the Caspian Sea as huge, fast-moving objects. The name Caspian Sea Monster was given by U.S. intelligence operatives who had discovered the huge vehicle, which looked like an airplane with the outer halves of the wings removed. After the end of the Cold War, the "monster" was revealed to be one of several Russian military designs meant to fly only a few meters above water, saving energy and staying below enemy radar.
The KM, as the Caspian Sea Monster was known in the top secret Soviet military development program, was over 100 m long (330 ft), weighed 540 tonnes fully loaded, and could travel over 400 km/h (250 mi/h), mere meters above the surface of the water.
The important design principle is that wing lift is reduced as operating altitude of the ekranoplan is increased (see ground effect). Thus it is dynamically stable in the vertical dimension. Once moving at speed, the ekranoplan was no longer in contact with the water, and could move over ice, snow, or level land with equal ease.
These craft were originally developed by the Soviet Union as very high-speed (several hundred km/hour) military transports, and were mostly based on the shores of the Caspian Sea and Black Sea. The largest could transport over 100 tonnes of cargo. The development of ekranoplans was supported by Dmitri Ustinov, Minister of Defence of USSR. About 120 ekranoplans (A-90 Orlyonok class) were initially planned to enter military service in the Soviet Navy. The figure was later reduced to less than thirty vehicles, planned to be deployed mainly for the Black and the Baltic Soviet navies. Marshal Ustinov died in 1985, and the new Minister of Defence Marshal Sokolov effectively ceased the funding for the program. The only three operational A-90 Orlyonok ekranoplans built (with renewed hull design) and one Lun-class ekranoplan remained at a naval base near Kaspiysk.