F3 machinery, two-shaft power, and the gap between peacetime and wartime speed

Was the F3 design intended to use three shafts with a separate cruising shaft?

No. The Royal Navy expected two shafts to carry the required power, with cruising and high-speed turbine arrangements serving each shaft rather than a dedicated center shaft.

The panel says the F3 design appeared to demand three shafts, yet surviving work indicates that the Royal Navy believed two would suffice. The shaft concept resembles the Nelson-class arrangement and implies more potential power than Nelson used historically. A cruising turbine optimized fuel economy while a high-speed turbine supplied maximum output, as visible in ships such as HMS Belfast. Published peacetime limits also understate what machinery might deliver in battle, because wartime crews accepted greater wear and risk; logbook distances remain difficult to convert into speed because ships zigzagged and operated in variable sea conditions.