We are examining organizational secrecy using the Manhattan Project during World War II as a case study. The Manhattan Project came about following the discovery of nuclear fission in 1938 and the understanding that Nazi Germany was trying to develop a powerful weapon that could change the course of the war. Naturally, the American effort had to be kept secret to hide both the existence of the project and, failing that, any information about progress and potential employment. How did they do it and what challenges did they face? What could we learn about maintaining secrets in contemporary organizations?