alt Hacker NewsIn the context of the time, those US scientists that built a reactor were all in for nuclear energy and absolutely 100% did not think that a nuclear weapon was economically feasible.
"Economically feasible" meaning maybe, perhaps, theoretically possible but even if so astronomically expensive in time, money, and physical resources.
It took the UK/CA/AU Tube Alloys group to find ways to make a weapon more practical, and multiple letters, attempts, and a one on one press the flesh tour to convince the US nuclear types that a weapon was both possible and achievable.
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The plutonium bomb was vastly more difficult to design than the uranium version.
Were both judged infeasible for different reasons? Perhaps uranium purification challenges and the implosion required for plutonium?
If you go to the Los Alamos Science Museum you can see an original letter from Albert Einstein where he proposed that a nuclear bomb could be fit on a ship and sailed into harbor in 1938. A ship-sized nuclear bomb was not of interest to President Roosevelt at the time for a likely good reason. It's only when the UK realized that it wasn't a ship size. It was something that you could drop from a conventional airplane bomber of the day that the US became interested.