The United States Secretary of Defense is the civilian head of the Department of Defense, a sprawling government agency which deals with military matters. As head of the Department of Defense, the US Secretary of Defense advises the President of the United States on policy matters, and he or she also works with the Joint Chiefs of Staff, who command the branches of the United States military. This position in the United States government is widely regarded as critical, because the Secretary of Defense has a huge influence on the direction of American military policy.
This is a Cabinet position, which means that the President appoints the US Secretary of Defense, and the United States Congress must confirm the appointment. The Undersecretaries who assist the Secretary of Defense are also subject to confirmation hearings. As with other Cabinet positions, the US Secretary of Defense is part of the line of succession to the Presidency; in the unlikely event that the President, Vice-President, Speaker of the House, President Pro Tempore of the Senate, Secretary of State, and Secretary of the Treasury were all incapacitated, the Secretary of Defense would become the President of the United States.
As a Cabinet member, the US Secretary of Defense must keep the President advised about important issues which may affect the security and well-being of the United States. Together with the President, the Secretary of Defense comprises the National Command Authority, which has the ability to launch nuclear weapons in the event that the President and the Secretary of Defense agree on such an action. The Secretary of Defense also oversees research and development, training, policies, spending, and other key aspects of the American military.
Policy is one of the most important facets of the work of the US Secretary of Defense. In addition to formulating sound policies for the American military, the Secretary of Defense must also be able to enforce policy, and to demonstrate the importance of such policy to the world. Policies handled by the Department of Defense can range from mundane issues, like proper haircuts for members of the armed forces, to critical decisions like how to handle nuclear weapons.
The position was created in 1947, and, by law, the Secretary of Defense must be a civilian who has not served in the military for at least a decade. Many Secretaries of Defense have had military service, although it is not required, and as of 2008, only one former General, George Marshall, had served in this position. Because the US Secretary of Defense or SecDef holds so much power, the position is considered to be among the “Big Four” on the Presidential Cabinet.