Abstract: An active, mechanical hydraulic control device for vehicles including watercraft and aircraft, comprises an acceleration pick-up having a relatively small mass. Movements of the mass are sensed by a nozzle and deflection plate system which controls as a preamplifier the displacement of a power drive member provided with one or more control apertures, the flow cross-sectional areas of which depend on the instantaneous position of a piston to which the power drive member is connected. The movements of the mass vary the gap width between the nozzle or nozzles and the deflection plate forming part of the movable mass. The change in the gap width controls the adjustment or displacement of the power drive member through a follower amplifier formed by the piston. The central or balanced position of the piston is assured by the control apertures forming respective piston position responsive valves.