In September 1966 an American spy satellite flew over a Soviet naval base on the Caspian Sea and took a series of photographs. The results created quite a stir among the American intelligence community. Their first guess was that this was a conventional aeroplane, possibly a sea plane, but one that was incomplete and much bigger than any aircraft the US had. But when the pictures were examined more closely, intelligence analysts calculated that, even if completed, it would actually fly really badly. This, coupled with the position of the engines, located well forward of the wing, made them realise what they were looking at was something entirely different.
They had stumbled on one of the most top secret military projects of the Soviet era. The object was soon dubbed the Caspian Sea Monster. What they were looking at was, in fact, an Ekranoplan; a wing in ground effect or WIG craft designed to fly at very high speed a few metres over the top of the sea. The Ekranoplan sits clean above the surface and relies on a well known, if little understood aerodynamic phenomenon called "ground-effect".
The bbc has an article and videos of the Ekranoplan in fight (including what seems to be a huge Soviet Ekranoplan in flight)."
Doubt is not a pleasant condition, but certainty is absurd. - Voltaire