Abstract: A surface effect vehicle has a propulsion and guidance system comprising a thrust generator (2) for producing a flow of fluid, a duct (7) adapted to receive the flow of fluid from the generator (2) and to conduct this to an outlet opening (11), a pair of rudders (14) mounted on opposite sides of the outlet opening (11) so as to be angularly adjustable relative to the outlet opening (11) to vary the extent to which they obstruct the outlet opening (11), and a rudder control system (17, 18, 19, 33, 34) adapted to move the rudders (14) together in the same sense between extreme angular positions in which the air flow is deflected to one side or the other of the outlet opening (11), wherein the rudder control system is adapted to move the rudders (14) in the opposite sense to one another so that they close together across the outlet opening (11) and thereby cause the fluid flow therefrom to be substantially progressively reversed.