The Department of Defense is part of the executive branch of the United States government. This Department was created in 1949, shortly after World War II. The department’s leader, James Mattis, was appointed by the president as the 22nd Secretary of Defense. The Department of Defense heads the armed forces and helps the president in the coordination of national security.The National Military establishment was created on September 18, 1947 by way of the National Security Act of 1947. These departments are the Department of the Navy, Department of the Army, and the Department of the Air Force. In 1949, and the name of the establishment changed to the Department of Defense. The first war department was then included into the Department of the Army. The military departments were then put under the Defense Department, without being considered a cabinet. The ability to overpower the military departments on operational subjects and the stating of the chain of command in the department came in the form of major amendment in 1953, 1958, and 1977.