In 1943, writer Cleve Cartmill proposed a story about a futuristic bomb to John W. Campbell, the editor of Astounding Science Fiction. Campbell liked the idea and gave him some background material on fission devices and uranium-235.
The story, “Deadline,” ran in Campbell’s March 1944 issue — and shortly brought a visit from the FBI. Apparently the technical details in Cartmill’s story had some uncomfortable resonances with the top-secret Manhattan Project, then under way at Los Alamos:
Two cast-iron hemispheres, clamped over the orange segments of cadmium alloy. And the fuse–I see it is in–a tiny can of cadmium in a beryllium holder and a small explosive powerful enough to shatter the cadmium walls. Then–correct me if I’m wrong, will you?–the powdered uranium oxide runs together in the central cavity. The radium shoots neutrons into this mass–and the U-235 takes over from there. Right?
Campbell explained that he’d studied atomic physics at MIT and had drawn the research from unclassified journals. In the end the authorities were satisfied — but they asked him not to publish any more stories on nuclear technology.