Technically modern subs are steam powered as well
neuc reactors produce steam to drive generators to produce electricity for propulsion some may even still use a steam propulsion system
we had daft terms in the navy which even to this day i have no clue what they were on about.
things like
COSAG Combined Steam And Gas Turbine
CODAG Combined Diesel and Gas Turbine
CODLAG Combined Diesel Electric and Gas Turbine
CODOG Combined Diesel or Gas Turbine
COGOG Combined of Gas or Gas Propulsion