If only we could get hold of a German atomic physicist, we felt, we could soon find out what the rest of them were up to. To us physicists the problem seemed very simple. Even those of us who were not working on the atom bomb project knew pretty well what was going on over here. No amount of military security could have prevented us from knowing, difficult as it was for the military to understand this. Active scientists engaged in the same general field of research inevitably form a kind of clan; they work closely together and know all about each other's specialities and whereabouts. You can't take a group of key scientists from their accustomed haunts and have them disappear in some remote place in New Mexico, together with their families, without their colleagues who are left behind wondering about it and deriving the right conclusions. The same thing, we knew, would be true of the Germans.