A German historian who controversially claims that the Nazis tested a nuclear device in 1945 has now unearthed a sketch of a "Nazi nuke", as the BBC puts it.
Rainer Karlsch's book Hitlers Bombe (Hitler's Bomb) rather sensationally suggests that German scientists detonated several nuclear bombs, the last in Thuringia on 3 March 1945. According to Karlsch, this destroyed around 500 square miles and killed several hundred POWs and concentration camp inmates.
Karlsch describes this development as a primitive "hybrid tactical nuclear weapon" - much smaller than those dropped on Hiroshima and Nagasaki - and claims to have amassed a weight of supporting evidence to back his assertion.
Other scientists are sceptical, asserting that the Nazi nuclear weapon programme was simply not capable of building a functioning bomb at that stage, however "primitive"*.
The new sketch - discovered in an undated report on German wartime nuclear research believed to have been compiled shortly after the end of the war in Europe - appears to show a plutonium device. Karlsch admits that the drawing is a simple schematic and does not prove the Nazis were building, or close to building a similar device.
He does, however, say that one small detail in the report regarding the amount of plutonium required to achieve critical mass is highly significant. The wartime head of Germany's nuclear programme, Werner Heisenberg, reportedly "failed to understand a key aspect of nuclear fission chain reactions".
As a result, he overestimated the amount of uranium required to build an atomic bomb. The newly-discovered report, though, states the roughly correct figure of 5kg of plutonium - leading Karlsch to assert that some German scientists were closer to Hitler's dream weapon than previously thought.
Professor Paul Lawrence Rose, of Pennsylvania State University and an expert on the German uranium programme, told the BBC: "Though it's wonderful to find the 5kg figure written on the document, one has to be sceptical about the rationale for it. Even if it's true and [some scientists] did understand it, Heisenberg's group wouldn't have accepted it." He added that it is possible that the report's unknown author may have gleaned the figure from the July 1945 Smyth Report into the US atomic weapons programme - something which Karlsch rejects.
Karlsch's article on the report, written in conjunction with Mark Walker, professor of history at Union College in Schenectady, appears in Physics World magazine. ®
*Rainer Karlsch says that the Nazi nuke was developed by a team led by physicist Kurt Diebner, working independently from Werner Heisenberg. Professor Rose calls this unlikely because "transcripts of conversations taped by MI6 when the scientists were held captive in England after the war showed Diebner lacked the knowledge to have done this".
Professor Dieter Hoffmann, of Berlin's Max Planck Institute for the History of Science, concurs: "Karlsch revealed some very important details in his book, but I can't go along with the picture he constructs with those details - of a Nazi nuclear test."