I think the proponents of the "German A-Bomb theory" place their faith in the Kurt Diebner program and discount Heisenberg. From what I can see the Diebner theory relies entirely on circumstantial evidence. I think the most telling fact that discounts bomb claims is that the Manhattan project was a multinational effort that cost about 30 billion dollars and needed thousands of scientist and a vast investment of resources. The Germans on the other hand had less than 100 scientist and a constantly shrinking resource base to work with. Also if they had a couple of A-bombs I think they would have tested them on the Russians regardless of how crude they were.
Even PBS is entertaining Diebner's theorist.
"During the last months of the war, a small group of scientists working in secret under Diebner and with the strong support of the physicist Walther Gerlach, who was by that time head of the uranium project, built and tested a nuclear device.
At best this would have been far less destructive than the atomic bombs dropped on Japan. Rather it is an example of scientists trying to make any sort of weapon they could in order to help stave off defeat. No one knows the exact form of the device tested. But apparently the German scientists had designed it to use chemical high explosives configured in a hollow shell in order to provoke both nuclear fission and nuclear fusion reactions. It is not clear whether this test generated nuclear reactions, but it does appear as if this is what the scientists had intended to occur".
http://www.pbs.org/wgbh/nova/hydro/close.html
I went to the NOVA site and read what was there. Their expert, Prof of modern German History Mark Walker, makes no case, at least on the NOVA page; it just asserts it. I don't believe it, for a number of reasons:
- The bomb diagram on the page there, while remeniscent of both the gun and implosion devices, seems to be neither. I don't see how it could work. The plutonium core was surrounded not by explosive but by "deckmantel" (cloak?), whatever that is; there's no sign of the fancy cast explosives that Fat Boy required. A slug of something is apparently shot into that to initiate the explosion. Considering the problems that Manhattan had in getting the implosion method right, I can't imagine his would do more than splatter extremely expensive plutonium everywhere. Thin Man required precise machining and a lot of experimentation, "twisting the dragon's tail", to determine how much metal was required for criticality. The choices of the metals used in the two designs was critical. And then there are the initiators.
-Where did they get plutonium? Over here we built huge reactors to cook U238 into Pl, then went through a chemical recovery ro strain it out of the U in quantities of fractions of a percent, and it made a hell of a mess on square miles of Washington real estate. The largest reactor found after the war was still 30% in size away from getting just to critical.
- Where did they get the uranium? The only sources at their disposal was from the Czech mines at Joachisthmal, and Belgian sources in Africa (cut off from Europe after the war started), that I know of. They confiscated a 1200 tons of Czech ore when they invaded Belgium, but it was all recovered by Alsos in it's original ore form, apparently untouched.
- Where did it get the heavy water moderator? You can't build a reactor without a moderator or bomb grade uranium/plutonium. They snatched 40 gallons of D2O in their invasions, but two separate sabotage events by the Norwegians spiked all the output of the Vemork plant for the rest of the war. Diebner stated, after the war, that:
When one considers that, right up to the end of the war in 1945, there was virtually no increase in heavy water stocks in Germany...it could be seen that the elimination of German heavy water production in Noway was the main factor in our failure to achieve a self-sustained atomic reactor before the war ended.
This lack of D2O, I think, was the main reason Heisenberg couldn't build a critical reactor. That, and he probably was dragging his feet heavily. BTW, Rhodes notes that Diebner and Heisenberg hated each other.
- Where's the radioactivity? We've ruined square miles of America building our bombs, and it would have been obvious to a trained investigator where those were, even without any knowledge about Manhattan. (We do know how to clean them up, of course, having 60 additional years and billions of dollars to learn how.) Testing of the soil in the area identified in Rainer Karlsch's book shows no sign of radioactivity.
- Where's the people who did the work? They all disappeared? They all clammed up, even after Germany's defeat? This, IMO, is where all conspiracy theories die; none can explain the needful, adamantly maintained security that fails only for the theorist. Diebner and Gerlag were picked up in Germany by Alsos, as were all the rest previously mentioned.
Wikipedia concludes that Diebner may have developed a dirty bomb. Apparently Walker is nearly all by himself in thinking Germany tested a nuclear weapon. Rainer Karlsch, a historian with a doctorate in economics, claims it was a combination fission/fusion device, which is ridiculous on its face, as the physics of fusion didn't yet exist, even in the Manhattan project, where it was only Teller's dream..