Until the National Security Act of 1947, the United States functioned without a Department of Defense. Matters of war and peace were handled by the Departments of War and the Department of the Navy while diplomatic aff airs were left to the secretary of state. With varied levels of success, the U.S. government managed to provide for national security and fi ght multiple wars, large and small, with a relatively small, resource-constrained bureaucracy. With World War II and the emergence of the Cold War, many of the so-called “wise men” responsible for U.S. security policies realized that never again could the United States aff ord to prepare for war, much less fi ght one, without a sophisticated organization capable both of advising the president and executing his policies using the nation’s military instruments. The threat posed by the Soviet Union, the peacetime challenge of administering a global strategy of containment, and the complexity of maintaining a well-trained, technologically sophisticated, and above all “ready” force required large staff of professional support and standard procedures grounded in law and practice.