There's a fascinating chapter on the discovery of Germany's "atomic bomb" and Japan's. Basically Germany's atomic bomb was some uranium percolating inside a cast iron pot submerged in some heavy water in a well; Japan's scientists needed some sort of electronic tube that was scarce and the navy had control over them since they were needed for some shipboard type stuff.
Niels Bohr, the Danish Nobel Peace prize in atomic studies (or something) said that America would have to turn itself into one gigantic factory to build a bomb. If you read the book, you'll find out that is exactly what we did.
You reference the Pulitzer-winning book I was about to mention in regard to the Axis atomic program. Neither the Germans nor Japanese were anywhere close to constructing a fissionable bomb package and these efforts were the first thing Allied investigators sought to learn about when these enemies surrendered.
The Germans intended their atomic program effort based at the Kaiser Wilhelm Institute to serve as a means of Naval propulsion or energy production; for a fissionable bomb they knew enough to perform the necessary theoretical calculations for the time and materials they’d need. They did the math, realized it was utterly hopeless, and gave up. All they had to show for themselves after the surrender of the Third Reich was an experimental nuclear pile which didn’t even meet pre-war achievements at the University of Chicago or UC Berkeley which were published in detail in science journals. Also, during the course of the war British MI-6 was doing heroic work in savaging the Nazi atomic fission program’s materiel resource accumulation. The Germans themselves did the most damage to their program by exiling all the top nuclear physicists from the Reich because they were non-Aryan: Fermi, Slizard, Meitner, Einstein, etc.
The Japanese effort was ultimately erased by the firebombing of Tokyo, but what evidence Allied investigators found in the rubble of Tokyo University amounted little more than an undergraduate’s chemistry set. Pre-war, they weren’t even in possession of a single gram of Radium in the manner that Marie Curie’s experiments required.
The Japanese physicists had endless trouble with the Imperial Japanese Navy and Army who saw the fission program as a silly diversion of budgetary capital and regarded the physicists in the program as a bunch of college eggheads who were unable to articulate any meaningful benefit in their research to the war effort. It hardly mattered since the Allied investigators realized the Japanese physicists were completely barking up the wrong tree in even constructing a functioning cyclotron for the Uranium separation method — another openly documented pre-war achievement journaled in science bulletins from Western nations. When the war ended, there were only one or two junior atomic physicists left alive in Japan to account to Allied investigators of their progress.
Neither the Germans or Japanese were going to possess an atomic bomb unless one was dropped on them by the Allies.