Abstract: The present invention provides a self-contained propulsion apparatus 1 suitable for a sub-sea ROV. The apparatus comprises: a reactor vessel 2 having at least one inlet 3, 4 and an exhaust 7; reservoirs 10, 11 for holding fuel and an oxidant material therefor, wherein the reaction products of said fuel and oxidant comprise steam; a remotely operable fuel and oxidant supply control device 12, 13; and a steam turbine 9 connected to the exhaust 7 so as to be driven by steam from the reactor vessel 2. The turbine 9 is drivingly connected 39 to a propulsion device 42 for propelling the ROV in use thereof. A degassing apparatus 17 is provided for substantially removing steam and any other gas phase reaction products, from the gas phase into the liquid and/or solid phase, downstream of the turbine 9.