Abstract: A sidewall gas-cushion vehicle is provided with a flexible skirt of hollow inflatable form, which, in operation of the vehicle, depends from the vehicle body so that the bottom of the skirt defines a convex face in close proximity to the surface over which the vehicle travels so as to form a plenum gap through which an atmosphere-seeking flow of cushion gas escapes. The flexible skirt is of two-stage form, comprising an upper compartment and a lower compartment. A fan, an aperture in a compartment-dividing membrane and an outlet duct are provided for inflating the lower compartment to a higher pressure than that existing in the upper compartment.