Only one of these beasts was ever built, the MD-160, in 1987. It saw about ten year of service before it was retired and put into a Kaspiysk boneyard.
It’s not an airplane, it’s not a boat, it’s just a “ship.” It can’t fly in a traditional sense but it doesn’t tread water either. It floats on a cushion of air between its wings and the surface of the sea. They are called Ground effect vehicles, or GEVs. Ground effect vehicles are still in manufacture today as they require less fuel to carry heavier payloads than traditional aircraft, even at aircraft speeds.
The idea was to move a boatload of troops and gear to a beachhead that had been neatly cleared in advance with six guided missiles, at 300 miles an hour.
If you want to know more about the MD-160 check out the Wikipedia entry for it. Here’s a long video detailing the history of Soviet GEVs. For the Lun-class ekranoplan skip to the 36:35 mark.