From English Russia:
An ‚Ekranoplan 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 ‚Äúmonster‚Äù 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.