With a POD after 1919, ...
I think a lot of people missed that key specification. This allows some possibilities for faster physics research in the 1920s & 30s. Its easy to say B could not be accomplished until A was established, and so on through the research of years. This is correct as far as it goes, but does not recognize the slow pace of the historical research, much of which was due to low funds and the time it took to obtain funds. The Mahatten Project accomplished what it did in 36 months due to the cash necessary for fast tracked parallel R & D tracks. Problems were buried under mountains of resources and blank cheques.
Lets imagine for a moment some eccentric billionaire is inspired by things like X Rays, electric lights, motors , ect that did not exist when he was a child. He invests massively in Curies laboratory, or your favorite physics research group, and draws in other investors. The result is the time to Fermis first atomic pile is shortened from 23 years to 17 or 18, with that critical experiment occurring circa 1937. From that a more measured and carefully managed atomic bomb project of 72 months can cost half or a quarter of the US effort & put these bombs in action 1942-44.