A metallic fuel mixture including solidic powders such as silicon, aluminum and magnesium together with an oxidant, and steam and hydrogen are fed into a combustor to undergo combustion therein. The combustor is positioned within a steam chamber enclosure filled with water as working fluid which is heated by the combustion. The heated water within the stream chamber enclosure is thereby converted into pressurized steam fed into a turbine for operation thereof to impart rotation to a shaft thereby propelling a sea vessel within which the steam chamber enclosure is housed. During such combustion, discharge from the combustor of a liquid by-product occurs as outflow through an exhaust funnel into a collector from which the by-product is processed for ejection into seawater without signature detection. The radiant energy generated by such combustion may be converted by photovoltaic cells within the steam chamber enclosure into electrical energy made available outside of the steam chamber enclosure, while some of the heat energy generated by the combustion within the combustor may also be converted by thermoelectric cells into electrical energy made available outside of the steam chamber enclosure.