Aage Bohr, “The War Years and the Prospects Raised by the Atomic Weapons,” pp. 191–214 in Stefan Rozental (ed.): Niels Bohr: His life and work as seen by his friends and colleagues (Amsterdam: North-Holland Publishing Company, 1967), on p. 193.
"After the outbreak of war and especially after the occupation of Denmark we in Copenhagen were completely cut off from following the allied nations’ efforts in the field of atomic energy. Various rumours reached us, however, of the German efforts, and the impression that in Germany great military importance was given to these possibilities was strenghtened by the visit to Copenhagen in the autumn of 1941 of Werner Heisenberg and C.F. von Weizsäcker. They were in Copenhagen on other business, but in a private conversation with my father Heisenberg brought up the question of the military applications of atomic energy. My father was very reticent and expressed his scepticism because of the great technical difficulties that had to be overcome, but he had the impression that Heisenberg thought that the new possibilities could decide the outcome of the war if the war dragged on.*
* In the book “Brighter than a Thousand Suns” by Robert Jungk it is asserted that the German physicists submitted a secret plan to my father, aimed at preventing the development of atomic weapons through a mutual agreement with colleagues in the allied countries. This account has no basis in the actual events, since there was no mention of any such plan either during Heisenberg’s visit, or during a later visit to Copenhagen – also mentioned by Jungk – of the German physicist Hans J.D. Jensen. On the contrary, the very scanty contact with the German physicists during the occupation contributed – as already mentioned – to strenghten the impression that the German authorities attributed great military importance to atomic energy."