A radiation-free heat source for early twentieth-century fleets

How would an early, radiation-free heat source equivalent to reactor fuel change warships and submarines before the Second World War?

It would transform propulsion, logistics, and global strategy, with scarce supplies concentrated in high-value fast ships and submarines rather than abolishing ordinary design limits.

The panel treats the hypothetical material as a non-radioactive nuclear-like heat source and immediately makes its deposits prime strategic territory. If plentiful, it would reshape power generation and ship propulsion before the world wars. If scarce, navies would reserve it for the assets that benefit most from endurance and speed, especially carriers, battlecruisers, and possibly submarines. The discussion also warns that a new heat source does not remove hull, armor, submergence, and machinery constraints, so not every imagined steam-powered submersible capital ship becomes practical.