A hydraulic propulsion system converts heat or thermal energy into hydraulic energy, and such hydraulic energy into mechanical work. The hydraulic propulsion system includes a thermal unit, a hydraulic cylinder with pistons and springs mounted therein, one or more hydraulic motors, one or more hydraulic accumulators, and one or more electrical energy generators, as well as a plurality of flow control valves to control the flow of hydraulic fluid between the various components. The hydraulic propulsion system may be enhanced by a sonic transmission unit including a sonic wave generator.