A longer review will follow, but Restricted Data is a close look at the practice of American nuclear secrecy. These days, we take the whole complex of classification as a fact of nature, much like the fissile possibilities of U-235. But of course, classification is whole artificial, a political system born out the Manhattan Project. And while classification may seem simple, a wall between the open ordinary world and the official secrets of the states, the reality is anything but simple.

The first regime of nuclear secrecy was purely voluntary. Leo Szilard recognized the military power of his idea of a self-sustaining nuclear reaction, and assigned the patent to the British royalty. As fascism role in Germany, he embarked on a not very successful campaign to halt publication on fission research. While pre-war activity could be tracked by who stopped publishing, the barriers to the bomb were primarily logistical. Only the United States could afford the expense of isotope separation and then bomb design. Classification in the Manhattan project was a system of compartmentalization, designed mostly to protect against leaks, and penetrated in key places by Soviet spies like Klaus Fuchs.

The category of Top Secret was actually invented for the Manhattan Project. Where the story gets weird is that immediately after the bombings of Hiroshima and Nagasaki, a concerted press effort from popular articles to the technical Smythe report discussed the bomb, create a world where some facts were public and others denied. The category of "Restricted Data" related to anything about science that could be used to make an atom bomb, basic scientific facts rather than the military secrets of defense plans and names of spies.

Since 1945, the story has been one of unwinding of secrecy, with categories of civilian nuclear science around power plants, and activist efforts to reconstruct the Teller-Ulam hydrogen bomb configuration from publicly available data in the 1970s. Modern nuclear non-proliferation is based on control of material: uranium ore and centrifuges, rather than control of knowledge. But even so, the world of nuclear secrecy is vast, a black monolith in a supposedly democratic state. Thinking about nuclear secrecy reveals many paradoxes.