The U.S. secretary of defense oversees the country's Department of Defense, the federal service responsible for the country's armed services and related military matters. This federal official acts as the principal defense policy maker and adviser. This position is similar to the minister of defense found in several other countries.

Main Duties

The secretary of defense exercises authority, direction and control over the three departments of the U.S. armed forces -- the Army and the Navy, as well as the Air Force.The main job of the U.S. secretary of defense is to plan, develop and execute policies that concern the military affairs and national security of the country. Also, such an official is responsible for the department's resource management and fiscal and program evaluation. The secretary of defense runs the entire department from the Office of the Secretary of Defense (OSD), which comprises the official's entire staff. The secretary's staff assists in carrying out assigned tasks in accordance with their job titles.

National Command Authority

The secretary of defense collaborates with the president to form the National Command Authority. This is a term that the U.S. military and federal government use to refer to the authority that these officials share regarding military orders, including the launch of nuclear weapons. As the commander-in-chief of the armed forces, the president is the ultimate authority. The secretary of defense's job is to allocate policies to the military departments, which train and equip the military forces; the chairman of the Joint Chiefs of Staff, who plans and coordinates military operations and deployments; and the unified commands, which conduct the military operations.

Supporting the Troops

The secretary of defense must ensure that all military services have the equipment they need and the equipment is integrated across all services. In addition, all troops must be properly trained in the use of the equipment and it must be appropriately allocated across the various services. If the U.S. decides to sell surplus equipment, the secretary of defense must ensure the recipient countries receive adequate training in its use.

Appointment

The secretary of defense is a member of the U.S. president's Cabinet, which consists of the most senior appointed officers of the country's executive branch. Like other cabinet members, the president appoints the secretary of defense with the approval of the Senate. The President cannot appoint a secretary of defense who has served as a commissioned officer of any of the country's armed forces within seven years from the date the individual was released from active duty.

Significance

The secretary of defense is considered one of the most important Cabinet members, next to the secretary of state, the secretary of the treasury and the attorney general. Also, the secretary of defense is sixth in the presidential line of succession--right after, in descending order, the vice president, the secretary of the treasury, secretary of state the president pro tempore of the Senate and the speaker of the House.