A propulsion system is disclosed that uses metal fuel particles heated to a range from 3000° K to 6000° K by reaction with oxygen in air inside a cyclone combustor to form metal oxides that are retained and removed from the combustor for re-conversion to metal, while nitrogen in the air is heated to the temperatures that on supersonic exhaust propels 50,000 ton monohull ships to from 50 to 100 knots. The ship can accelerate by electromagnetic force from a MHD generator-accelerator rendered electrically conducting by alkali metal seed injection into the gas. Also disclosed are 10 MW to 1000 MW Closed Cycle MHD power plants fired by natural gas into a top half of a falling pebble bed heat exchanger that transfers 2000° K to 3000° K heat to a noble or diatomic gas in a bottom half of the exchanger that on exit is seeded with an alkali metal rendering the gas conducting.