Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

This is a very good observation from Brent.
The catalog is an issue from 1935, so long before WW2, and even before the USA got involved in 1942, after Pearl Harbor.
So, it's not likely that this engine is a direct reflexion of the war effort.
By 1945 Nuclear power was the new technology that all the efforts went too.
And it took until 1952, before work started at the Nautilus, that was delivered to the US Navy in 1954.

So why would a toy company, and it was depicted in a toy catalog, call it a submarine engine?
https://archive.org/details/EmpireEducationalToys1935/mode/2up
I don't know enough on the experimental development history on US subs.
But, was there any abandoned sub Stirling engine project in the 1930's the the world has forgotten about?
Or where these empire engines also used by the navy in 1930's submarines to run something?
I think those could be the closed explanations.
But It still remains a big mystery…

Cheers,
Danny