National Security Act of 1947

National Security Act of 1947, United States federal law that set up the National Military Establishment, headed by a secretary of defense who holds Cabinet status. The National Military Establishment was renamed the Department of Defense in 1949. Following World War II (1939-1945) American political leaders began an effort to consolidate U.S. armed forces under a unified command that would coordinate all branches of the military. Before 1947 the Army (which included the Army Air Forces) and the Navy had operated as separate entities with no permanent coordinating command structure. The National Security Act of 1947 created a unified National Military Establishment.

The legislation established the United States Air Force as a separate branch of the armed forces and placed the secretaries of the Army, the Navy, and the Air Force under the direction of the secretary of defense. The Joint Chiefs of Staff, consisting of representatives from the three services, assumed responsibility for strategic planning and coordination. A 1949 amendment to the act increased the powers of the secretary of defense and created the position of chairman of the Joint Chiefs of Staff. These changes further centralized the organization of policy among the three branches of the military.

The act also created the National Security Council (NSC), whose members are drawn from government departments and military positions, to advise the president and Congress on national security. Directly responsible to the NSC was the Central Intelligence Agency (CIA), which evolved from the wartime Office of Strategic Services. The CIA took on the duties of intelligence gathering and analysis related to national security. A number of research and development organizations established shortly after the passage of the act did not survive. However, a 1958 amendment to the act created the position of director of defense research and engineering to guide high technology projects.