Abstract: According to the invention, inflatable buoyancy bodies are kept in storage housings on the outside of a vehicle. During normal use, buoyancy bodies are folded up and stored under covers. Only when the vehicle is on water do the covers open and buoyancy bodies fill with air. An on-board compressed air system supplies air for filling buoyancy bodies so that air, which is not required by a braking installation or the like of the vehicle, is used to fill the buoyancy bodies. The additional use of outside air enables more air to be supplied to the buoyancy bodies at a low pressure than the sole use of the on-board compressed air system. In order to empty the buoyancy bodies, a vacuum is generated in connection lines. When stop cocks are open, air is sucked out of the buoyancy bodies, which then fold up and the covers are closed and locked.