The Office of Censorship's struggle to keep journalists from revealing the development of the first atomic bomb, the sites where the development was taking place, and the fact that the bomb might be available for use in the war, was desperate and in many ways heroic. Soon after it was created on December 19, 1941, the office issued a voluntary wartime code of practices for newspapers, magazines, and periodicals which asked editors to act according to whether they thought the information in their possession was of use to the enemy. For the next three years the appearance of stories on heavy water and atom smashing became a problem which the Office of Censorship had to monitor continually by issuing confidential notes to editors of newspapers and weeklies as well as managers of radio stations. The Office of Censorship also was frantically battling leaks outside of mainstream magazines and newspapers, such as book publishers, "appropriate authorities," and universities. This lasted until the atomic bomb was dropped on Hiroshima on August 6, 1945, at which point the Office of Censorship's Press Division took the view that virtually anything was permissible except a description of how the atom was split or the internal workings of the bomb. Remarkably, throughout the war, the press did bear with the government policy of revealing virtually no technical details about the bomb, primarily because it enthusiastically supported the war. The voluntary form of censorship had worked. (Seventy-three notes are included.) (MS)