<P> The Department of Defense is composed of the Office of the Secretary of Defense (OSD), the Joint Chiefs of Staff (JCS) and the Joint Staff (JS), Office of the Inspector General (DODIG), the Combatant Commands, the Military Departments (Department of the Army (DA), Department of the Navy (DON) & Department of the Air Force (DAF)), the Defense Agencies and Department of Defense Field Activities, the National Guard Bureau (NGB), and such other offices, agencies, activities, organizations, and commands established or designated by law, or by the President or by the Secretary of Defense . </P> <P> Department of Defense Directive 5100.01 describes the organizational relationships within the Department, and is the foundational issuance for delineating the major functions of the Department . The latest version, signed by former Secretary of Defense Robert Gates in December 2010, is the first major re-write since 1987 . </P> <P> The Office of the Secretary of Defense (OSD) is the Secretary and Deputy Secretary's (mainly) civilian staff . </P> <P> OSD is the principal staff element of the Secretary of Defense in the exercise of policy development, planning, resource management, fiscal and program evaluation and oversight, and interface and exchange with other U.S. Government departments and agencies, foreign governments, and international organizations, through formal and informal processes . OSD also performs oversight and management of the Defense Agencies and Department of Defense Field Activities . </P>

All functions in the department of defense and its component agencies are performed under