German Nukes
PaxMondo:
there was some serrendipity [USA] and some human error [GER] both involved.
In the case of the west you can see some progression with more experimental data refining the data, yielding better quality numbers. As I recall, the final calculation was in the tens of pounds and the designers padded that to about 100 pounds of fissile material. There is a coding question about how to apply a randomization factor on a technical advance (duration of 200 days +/- 50 days) or make success problematic. I don't know how to do that. But I can see about putting together a tree.
PaxMondo:
How much of a supporter [of the Nazi's] was he, and is there any evidence that the calculations were muffed on purpose?
In 1938, the SS investigated him because he had enough scientific integrity to refuse to knuckle under to some ideological German scientists who were dismissing quantum physics as a "Jewish" science. Heisenburg was cleared. He visited the USA in the summer of 1939 and was besieged with offers to come to the USA and teach like Fermi, Szilard, and others. He refused all offers.
Heisenburg was disillusioned about the prospect of democracy to oppose the great dictators. His belief was that the totalitarians would win. Given that decision, he decided that a German world empire would be better than the Soviet alternative. Some apologists for Heisenburg have suggested he did intentionally fumble the calculations, but the transcripts from the interrogation suggest that at the least he continued acting as if this was a colossal blunder instead declaring with relief he could "end the charade."
Heisenburg was a great theoretician, but was sub-par when it came to creating practical applications. I think that was critical problem for the German program - he was the wrong guy to head the program.
PaxMondo:
But IIRC, the GER team did know about the concept of Alpha particle asorbtion to control the reaction [control rod theory].
I took a second look at the drawing, and it seems that the premise was that you could have two halves of the spherical paraffin/uranium core and then bring them together with the volume of heavy water between the two halves serving as the moderator. The failure mode with that is if you lost track of the temperature and started boiling the water, then you replace the heavy water with less dense heavy-water steam. If you don't move the core halves then you the possibility of a run-away. The engineering solution is a kill switch that uses springs or counter-weights to return the core halves to their start positions at a safe distance in the heavy water tank.
Events:
1) Initial unsucessful British Commando Raid on Heavy Water Plant (slight chance for success, burns supplies)
2) Subsequent unsuccessful British spy raid on Heavy Water Plant (slight chance for succes, burns fewer supplies)
3) Subsequent unsuccessful British bomber raid on Heavy Water Plant (slight chance for succes, burns oil and supplies)
4) Second spy raid on Heavy Water Convoy taking inventory to Germany (slight chance for success, burns supplies) (historical success in sinking the ferry where the heavy water rail cars were.)
5) Special do or die bombing raid on Berlin nuke labs (ahistorical) (moderate chance for success, burns supplies, oil, and manpower).
6) Heavy Water Pile Meltdown (ahistorical) (slight chance of simulating a dirty nuke hit on Berlin (or Moscow or Tokyo or Cambridge or Chicago or Paris) if a heavy water pile is achieved).
7) Heisenburg defects in 1939 (ahistorical) (A slight chance that the USA get a nuke tech but the Germans don't make the tons of uranium mistake and can move past the bomb mass miscalculation).
8) Nuclear Secrets Spying (historical) (Probably, the right way to do this is to have a small probability that whenever the USA or Britain discover a nuclear tech, it may be stolen by the Russians. The US compartmentalized their research so only a handful of trusted individuals knew it all. The British moved their people around and got more use out of them. Klaus Fuchs penetrated the British sysem and gave the Russians a stream of technology on diverse topics. Russian agents in the USA tended to get or not a single item).