Saw a show about that on the History Channel. Pretty cool idea. Wonder if it could be made to carry a ton of firepower and how well it would work on relatively rough seas. Would make a decent attack unit for coastal operations.
It is using the "Ground effect".
You have not only the normal effect, how each wing is working, also the air is compressed between the ground and the wing.
This effect is extremly strong but works only for few meter high over the ground.