Comment by defrost

In truth the Chicago Pile crowd were all about power generation and didn't think it was feasible to make a nuclear bomb ..

( Not impossible, more strictly "beyond reach" economically and processing wise, operating on over estimates of the effort and approach )

They ignored letters from Albet Einstein on the topic, they ignored or otherwise disregarded several letters from the Canadian / British MAUD Committee / Tube Alloys group and it took a personal visit from an Australian for them to sit up and take note that such a thing was actually within reach .. although it'd take some man power and a few challenges along the way.

* https://en.wikipedia.org/wiki/MAUD_Committee is one place to start on all that.