The National Security Act of 1947 established the Department of Defense (named the National Military Establishment between 1947 and 1949) as part of a new national security structure for the United States. Exactly a half century after James V Forrestal took the oath of office as the first secretary of defense, the Department of Defense marked its 50th anniversary on 17 September 1997. This book presents a 50-year history of the evolution of DoD organization and the top leadership of the department. The higher organization of the department has evolved from the small office of the secretary of defense and three special assistants established in 1947 to a formal Office of the Secretary of Defense, now including more than 2,000 persons. As this study shows, developing an effective department-wide organization concerned Forrestal and most of his successors. Major reorganizations took place in 1949, 1953, 1958, and 1986, with important Incremental changes occurring over the years This hook discusses specific organizational issues, such as civil-military relations, the roles and missions of the armed forces, the positions of the service secretaries, and the organization and duties of the Joint Chiefs of Staff, especially its chairman.