The Department of Defense is responsible for maintaining and overseeing government organizations that relate to the safety of the United States. The Department of Defense governs all branches of the U.S. Military to ensure the protection of the country.
The Department of Defense's top priority is the security of the United States, and it provides the military forces needed to enforce that goal. The Navy, Marine Corps and Army were separate entities until 1947 when they were consolidated into one department known as the National Military Establishment. The organization changed its name to the Department of Defense in 1949.
The Coast Guard, Air Force and Guard Reserve are also part of the Department of Defense. The infrastructure is considerably larger than those organizations, and includes the National Security Agency, the Defense Intelligence Agency, Missile Defense Agency and Homeland Security.
The headquarters for the Department of Defense is located in the Pentagon, located in Washington, D.C. The organization has a big job to do, understanding that the protection of the U.S. includes a significant global presence, and there are commands in other areas and countries, including the Middle East, West Asia, Africa, Europe, South American, the Caribbean, the Mediterranean and Canada.