I was in Los Alamos for less than a year. Well, I came in the beginning of 1944, and left by the end of 1944. As soon as I came to Los Alamos, I realized that my fear about the Germans making the bomb was ungrounded, because I could see the enormous effort which was required by the American[s], with all their resources practically intact, intact by the war — everything that you wanted was put into the effort. Even so, I could see that it’s still far away, and that by that time the war in Europe was showing that Hitler is going to be defeated, and I could see that probably the bomb won’t be ready; even that Hitler wouldn’‘t have it in any case. Therefore I could see this from the beginning, that my being there, in the light of the reason why I came to work on it, was not really justified. But nevertheless, I could not be sure that the Germans would not find a shortcut maybe and they could still make the bomb. Therefore I kept on working together with the other people, although I was very unhappy about having to work on it. But as soon as I learned, towards the end of 1944, that the Germans have abandoned the project, in fact a long time before, I decided that my presence there was no longer justified, and I resigned and I went back to England.

Martin Underwood, Joseph Rotblat: a man of conscience in the nuclear age, Brighton [England] ; Portland, Or, 2009, p. 29