The National Security Act of 1947 was a major restructuring of the United States government's military and intelligence agencies following World War II. The majority of the provisions of the Act took effect on September 18, 1947, the day after the Senate confirmed James Forrestal as the first Secretary of Defense. His power was initially limited and it was difficult for him to exercise the authority to make his office effective. This was later changed in the amendment to the act in 1949, creating what was to be the Department of Defense.