Only a few decades ago navy ships would have been oil fired boilers with steam turbines. Adjusting throttles wasn't a case of moving a lever. A valve had to be

Only a few decades ago navy ships would have been oil fired boilers with steam turbines. Adjusting throttles wasn't a case of moving a lever. A valve had to be moved by hand, changing the flow to the turbine. This had to be done in concert with the guys in the boiler room. Doing so may have required lighting up a number of extra burners in the boiler or changing the size of the nozzles in use. Of course modern diesel engines are more flexible. You might still have to fire up the gas turbines on a modern navy vessel which would at least require checking oil etc. The systems in use likely haven't evolved far for a number of reasons.