An ekranoplan is a seagoing vehicle similar in function to a hovercraft. Like a hovercraft, it flies on an air cushion, but there the similarity ends. An ekranoplan is more like an airplane in looks and operating principle. It uses an effect of aerodynamics called ground effect to keep itself out of the water. It looks like a plane flying just above the water, but due to the ground effect, it is more energy efficient.
The big problem with ekranoplans is getting out of the water, which requires very high speeds. Because of the enormous drag of water, some ekranoplans have several extra jet or propeller engines only used to get out of the water.
Once out of the water, some can also travel over flat land.
The first ekranoplans were built by the Soviet Union in the 1960s, but since then, ekranoplans have also been built in the USA, in Japan, China and Germany.
Most ekranoplans built are rather small, but there are a few exceptions. Most notably, the "Caspian Sea Monster" or "KM" , a 550 ton Sovjet vehicle capable of reaching speeds of 500 km/h and heights of 20 m above the waves. By comparison, a Boeing 747 has a maximum takeoff weight of 400 tons. Go find a picture of the Sea Monster - it's impressive.
The expression "ekranoplan" is a Russian compound word of "ekran" - screen and "plan" - plane (aircraft). Another word for ekranoplan is the abbreviation "WIG" - Wing In Ground effect.