The CIA dubbed them the "Caspian Sea Monsters" (one might think because US government spy satellites and overflights spotted these gargantuan beasts skimming across the Caspian Sea but more likely the name came from intelligence "agents" who witnessed the things in what amounts to full flight). The Soviets called them KM. Known as ekranoplan (Russian экранопла́н "screen plane"), these ground effect craft (GEV- ground effect vehicle) were designed to exploit two advantages of low-level flight - the low-propulsion requirements of ground effect flight (WIG - Wing in Ground effect), and the ability to fly below radar coverage.
The Soviets designed, developed and built a range of these huge GEV. They built troop carriers, military transports and they even built versions that operated as (extremely) mobile missile launch platforms. The largest, the KM, weighed some 540 tonnes fully-loaded and could carry over 100 tonnes of cargo (that's as much as a Boeing 757!.
These were some big, bad, battle-cruisers. The only thing they lacked were those cool, robotically-controlled laser guns you see in the movies. Oh, and the ability to jump to warp speed. But no doubt the Soviets had that well in hand too. Damn you, Reagan. DAMN YOU!
Not to worry, the Chinese are on the case.
Not had enough? There is some cool Google Earth-related stuff here.