An energy supply system which utilizes a vaporizing chamber containing a vaporisable liquid. A heat source is supplied to vaporize the liquid which drives an engine to produce mechanical energy. A condenser is connected to the engine to condense the vapor back to a liquid, which is then fed back to the vaporizing chamber. The mechanical energy is used to supply usable electrical energy and to power an electrolysis plant which separates water into its constituent parts. The constituent parts are stored for subsequent energy-creating recombination in an electricity-producing fuel cell and/or a heat energy-producing underwater burner. The heat energy produced by the underwater burner is used to heat a water supply surrounding the burner.