The US built a reactor first too [1], followed by others [2] as part of the Manhattan Project.
[1] https://en.wikipedia.org/wiki/Chicago_Pile-1 [2] https://en.wikipedia.org/wiki/Hanford_Site
[1] https://en.wikipedia.org/wiki/Chicago_Pile-1 [2] https://en.wikipedia.org/wiki/Hanford_Site
"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.
Some time later Mark Oliphant visited the US in person and walked key people through a circles and arrows on chalkboard breakdown of how such a thing would be actually possible.
Also, Tokyo Bay.
For the Axis powers, it would be an even easier sell of course.
At least if any of them could believe - or even imagine - that it actually could exist or be as devastating as it was of course. And frankly, unless you saw the footage of an actual Tsar Bomba, how could anyone?
For the first bomb ever made to immediately jump to Tsar Bomba size, or for it to utilise an understanding of fallout and contaminants that didn't exist prior to the Castle Bravo tests seems ... unlikely.
I think you’re making my point though - literally no one could really comprehend or believe such a thing was even possible. Ever.
Until they saw it happening.
So of course it got dismissed until it was essentially inevitable.
The Tsar Bombe footage* had warships in the frame for scale? That's certainly news to me.
> the scale is obvious to anyone who has seen explosions/bombs before.
Okay, fair point - so how big or small was this nuclear explosion then? (No banana for scale, but there is a human for reference): https://i0.wp.com/blog.nuclearsecrecy.com/wp-content/uploads...
Sure, there's no real challenge to lookup the test series via name in the URL for answers, but bear in mind, watching live IRL as the bubble expands the question for casual humans is how far away is that explosion? ( Fermi had distance, time, and shockwave force at distance to work with: https://en.wikipedia.org/wiki/Fermi_problem )
* 1961 Tsar Bomba hydrogen blast: https://www.youtube.com/watch?v=YtCTzbh4mNQ
Were both judged infeasible for different reasons? Perhaps uranium purification challenges and the implosion required for plutonium?
The Frisch–Peierls memorandum changed that understanding ... provided that reading of the FP-memorandum was convincingly conveyed to people that made things happen, what Einstein put to paper (and was ignored) and that Oliphant pushed through in person.
Little Boy on Hiroshima was a gun design, a grossly inefficient McGyver that used some 64 kilograms of enriched uranium to successfully convert less than half a gram to energy.
Fat Man on Nagasaki was an implosion device - a necessary design change due to simply not having enough uranium or an enrichment pipeline to sustain the needs of a gun design.
The first device detonated, at Trinity in the USofA, was an implosion device, created to test the more difficult design.
Further, there was an abandoned / discarded "Thin Man" device IIRC.
These were all alternative implementations that were pursued after the FP-memorandum was pushed about to make the case that weapons were apparently possible rather than not yet achievable - the prevailing belief in the US prior to Oliphant doing the rounds.
These weapons were, however, as different as their monikers imply. Little Boy was a uranium, gun-type weapon, whereas Fat Man was a plutonium, implosion-style weapon. Two types were needed because there was only enough uranium for one gun-type weapon, and the U.S. government knew it would need to make more than one weapon.