[mandevil]

The Nth Country Experiment, in 1964, took three freshly minted Physics Ph.D's without any security clearances of any kind, gave them access to a reasonably sized unclassified physics library, and asked them to design an implosion weapon. After approximately three man-years of effort (along with some basic calculation assistance from some 1964 unclassified calculators) those Ph.D's designed a workable implosion bomb. So by 1964 it is clear that design was not the limitation: every real country can scrape together a few Physics Ph.D's for three man years of effort.

I would STRONGLY disagree that the Germans were ever more advanced than the Manhattan project. The British were a bit (~9 months) ahead of the US before S-1 started (December 1941), but I've never seen any evidence that the Germans were ahead of either country at any point. Certainly the fact that they never managed to replicate CP-1, which went critical in December 1942 (and was still years of hard work away from an actual nuclear bomb) suggests that they were never very close at all.

The closest I can come up with is that the discovery of nuclear fission in 1938. In that work, there were five people who collaborated closely enough that today they would have all had their names on the one paper (because of Nazis the work was published in two papers, Aryans on one, Jews on the other): Otto Hahn, Fritz Strassman, Lise Meitner, Otto Frisch, and Wilhelm Traube. Hahn and Strassman were considered Aryan enough to stay in Germany. Meitner and Frisch escaped- Frisch ended up working on the MAUD report and then at Los Alamos, Meitner stayed in neutral Sweden. Traube did not manage to escape and died in Gestapo custody in 1942. So 20% of this team ended up at Los Alamos, and only 40% managed to stay in Germany, which does somewhat point to some of the underlying problems any German bomb project would have had.