United States Military Establishment.

National Military Establishment

After the end of World War II, President Harry Truman proposed the creation of a unified department of national defense. In a special message to Congress on 19 December 1945, the president cited both wasteful military spending and inter-departmental conflicts. Deliberations in Congress went on for months focusing heavily on the role of the military in society and the threat of granting too much military power to the executive.^[16]

On 26 July 1947, Truman signed the National Security Act of 1947, which set up a unified military command known as the "National Military Establishment", as well as creating the Central Intelligence Agency, the National Security Council, National Security Resources Board, United States Air Force (formerly the Army Air Forces) and the Joint Chiefs of Staff. The act placed the National Military Establishment under the control of a single secretary of defense.
 The National Military Establishment formally began operations on 18 September, the day after the Senate confirmed James V. Forrestal as the first secretary of defense. The National Military Establishment was renamed the "Department of Defense" on 10 August 1949 and absorbed the three cabinet-level military departments, in an amendment to the original 1947 law.

Under the Department of Defense Reorganization Act of 1958 , channels of authority within the department were streamlined while still maintaining the ordinary authority of the Military Departments to organize, train, and equip their associated forces. The Act clarified the overall decision-making authority of the secretary of defense with respect to these subordinate Military Departments and more clearly defined the operational chain of command over U.S. military forces (created by the military departments) as running from the president to the secretary of defense and then to the unified combatant commanders. Also provided in this legislation was a centralized research authority, the Advanced Research Projects Agency, eventually known as DARPA. The act was written and promoted by the Eisenhower administration and was signed into law 6 August 1958.