From Wikipedia:
The Lun-class Ekranoplan is a ground effect vehicle (GEV) designed by Rostislav Evgenievich Alexeyev in 1975 and used by the Soviet and Russian navies from 1987 until sometime in the late 1990s.
It flew using the lift generated by the ground effect of its large wings when within about four metres (13 ft) above the surface of the water. Although they might look similar to regular aircraft, and have related technical characteristics, ekranoplans like the Lun are not aircraft, seaplanes, hovercraft, nor hydrofoils. Rather, “ground effect” is a distinct technology. The International Maritime Organization classifies these vehicles as maritime ships.