The Secretary of Defense is the principal defense policy advisor to the President. Under the direction of the President, the Secretary exercises authority, direction, and control over the Department of Defense. The Deputy Secretary, the second-highest ranking official in the DoD, is delegated full power and authority to act for the Secretary and to exercise the powers of the Secretary on any and all matters for which the Secretary is authorized to act. The
Department of Defense is America's oldest and largest government agency. With our military tracing its roots back to pre-Revolutionary times, the Department of Defense has grown and evolved with our nation.