Heisenberg. There was a very influential thesis by Paul Rose that Heisenberg tried to help the Nazis get the A Bomb. I mentioned before that I think that clearly he did the opposite. This paper by Carl Meyer shows in detail what I have thought for a long time--that Heisenberg easily could work out how much U235 was needed and yet always over estimated it in conversations to show that it was impossible for the Germans to get that much. [Han complained to him that his estimates varied from 50 kilos to 2 tons.] Albert Speer specifically asked Heisenberg about it and came away saying the Heisenberg convinced him that it was impossible.[Besides all this, it ought to be noted that the paper by Paul Rose has a flawed analysis of how to get to the critical mass. It was not written by an expert in atomic fission.]
Besides that in his 1939 paper, he ignored the actual question that was asked to him if it is possible to make a bomb out of Uranium. Instead spent the entire paper discussing making a nuclear reactor to create energy. [He did mention twice the idea of explosives in his 41 page paper with no approximations nor math. He just said pure U-235 would be needed for that.]
But at Farm Hall when asked how much was needed he gave a lecture on Aug 14 1945 and came up with the 6.2 square centimeters value. I.e. when he really wanted to know, he could easily work out the value. When he did not want to know and wanted to discourage others, he came up with fanatic amounts that were impossible to get.
https://www.nybooks.com/articles/2001/02/08/heisenberg-in-copenhagen-an-exchange/
