This isn't a scientific forum but the German experimental reactor was to use the heavy water,rather than graphite, as the moderator.
That´s pretty clearly a set of incomplete informations to a degree that we today have to call it incorrect.
Correct is that some experiements carried out in Leipzig initially tried with graphite (the theory behind was understood) but then shifted to heavy water due to impureness of the then used graphite. However, before 1943 and 44, both Heisenberg and Diebner used pure graphite and heavy water in combination for moderation, indicating that the purpose of graphite moderation wasn´t completely abandoned. Thus, the pile which went critical in Gottow 1944, Diebners 4th experiement used spehrical orientation of U-238 cubes, heavy water and graphite shields for moderation.
That´s much further than was known before and Karlsch certaily deserves credit for isolating the primary sources in Moscow for these events. Other claims are dubious as far as interpretations go. The radioactive isotopes found in Thuringia, used by him to proove a nuclear event, f.e. were not found to discriminate from the local background radiation in analysis conducted by the MPA. However, those of Gottow did and confirmed a nuclear event there. Diebener´s experiemental pile went critical and in principle solved what is required for plutonium extraction, Heisenberg at Haigerloch couldn´t succeed with a critical reactor- in part because some of the fissionable material and heavy water was still at Thuringia when he commenced his experiements ´45. Interestingly, Heisenberg reverted to Diebners spherical orientation of uranium cubes in his last experiments.
Heisenberg may have deliberately tried to stall the advances in creating a bomb by calculating a much higher than required critical mass. All his experiemtns were aimed on power generation rather than a nuke. However, KWI conference papers from 1943 already proove that Ardenne and Diebner established a correct calculation of the critical mass. Diebner was an Army scientist, von Ardenne lead the group of the Post (mail) services, which had their own nuclear program and concentrated on uranium enrichment facilities. He later became instrumental in the creation of the first soviet nuclear pile (buildt up completely from material captured in eastern Germany).
Much more work was done than previously known. However, several He-177A5 (Werknummer 550001 to 550006) were modified with a single, very large bombbay and often are incorrectly interpreted to be carrier of a nuclear weapon. However, the purpose may still be as simple as a very large conventional bomb.
They *could* have carried a nuke similar to US ones but such a weapon did not exist in Germany in 1944 or spring 1945. Karlsch´s research does make this clear.