The United States Department of Defense (DoD) is an important federal department which deals with coordinating and supervising all agencies directly involved with national security and military affairs. The DoD is one of the largest tenants at The Pentagon and is made of three chief sub-departments, the Department of the Army, the Department of the Navy and the Department of the Air Force.
Alternative DOD departments include the National Geospatial-Intelligence Agency (NGA), the Missile Defense Agency, the Defense Advanced Research Projects Agency (DARPA), the Pentagon Force Protection Agency (PFPA), the Defense Intelligence Agency (DIA) and the infamous National Security Agency (NSA).
In terms of the department’s history, it was established based on some specific plans put forth by the Joint Chiefs of Staff and on 19 December 1945, President Harry S. Truman proposed the creation of a brand new unified Department of National Defense. The proposal was argued over and was not passed until 1947.
On July 26, 1947, Truman passed the National Security Act of 1947 which set up the National Military Establishment which would begin active operations in September, 1947. The Establishment had the ill-fated abbreviation NME which sounds very much like ‘enemy’ and it was, in 1949, baptized the DoD.
Until the creation of the DoD, US armed forces were divided into varied departments which lacked any real central authority. The Marine Corps remained as a separate service under the control of Naval Department while the Coast Guard remained under the control of the Treasury Department.
The DoD’s budget was around 7 billion in 2007 though this figure does not include tens of billions more in supplementary spending on things like nuclear weapons tests.
In times of war, the Department has authority over the Coast Guard. According to the US Code, the Coast Guard is always considered one of the five branches of the US armed services. During times of proper war the Coast Guard works as a section of the Navy even though the Coast Guard has not been under the full control of Navy since World War 2.
The official command structure of the Department is determined by the Goldwater-Nichols Act of 1986, which was signed into law by President Ronald Reagan in October, 1986. The Act altered the command of the US military and it introduced the most distinctive changes to the Department since it was established.
According to the Act, the command structure passes from the US President, through the Secretary of Defense, to the commanders of all military forces (COCOM). The Chairman of the Joint Chiefs is most responsible for readiness of the US military and behaves as the President’s military adviser while remaining firmly outside of the chain of command.