Tommy Franks and Donald RumsfeldGen. Tommy Franks (left), commander in chief of Central Command, with U.S. Secretary of Defense Donald Rumsfeld, 2002.(more)The civilian secretaries of the military departments (Army, Navy, and Air Force) are responsible for the administration of their particular departments and are responsible for training, equipping, and providing combat-ready forces to the combat commands. The combat forces of the Army, Navy, Air Force, and Marine Corps are under unified combat commands, organized on either a geographic or a functional basis. A unified command contains combat forces from more than one service, such as Central Command (CENTCOM), which is composed of all Army, Navy, Air Force, and Marine Corps units in Central and Southern Asia and the , or Special Operations Command (USSOCOM), which oversees .Joint Chiefs of StaffPres. Barack Obama (his back to the camera) holding a meeting with the Joint Chiefs of Staff in the Oval Office concerning the repeal of "Don't Ask, Don't Tell," November 29, 2010.(more)The commanders of the unified commands are responsible to the president and the secretary of defense. By secretarial delegation, the Joint Chiefs of Staff exercise operational direction over the unified commands. The Joint Chiefs of Staff are the principal military advisers to the president, the , and the secretary of defense. The Joint Chiefs of Staff consist of the chairman, Joint Chiefs of Staff, who is the nation’s highest-ranking military officer; the vice chairman; the chief of staff, United States Army; the chief of naval operations; the chief of staff, U.S. Air Force; the commandant of the Marine Corps; and the chief of the National Guard. The chiefs are appointed by the president to four-year terms. The Joint Chiefs of Staff are supported by the Joint Staff, which is limited by law to not more than 400 officers. This staff is organized along conventional military staff lines, and performs such functions as developing strategic concepts and war plans, reviewing the operating plans of the unified commands, and establishing unified doctrine for operations. An assignment to the Joint Staff provides military officers a unique opportunity to work on coordinated plans and to develop an understanding of the integrated effort required under the modern concept of joint operations.National Security AgencyNational Security Agency headquarters, Fort Meade, Maryland.(more)National Reconnaissance OfficeNational Reconnaissance Office headquarters in Chantilly, Virginia.(more)In the early 21st century there were 20 defense agencies within the Department of Defense. These agencies were established to provide integrated and unified effort in support activities that generally cut across service lines. The defense agencies have consolidated functions that were previously fractionalized among the military services. Among these agencies were the (NSA), which held responsibility for signals intelligence and ; the (DARPA), responsible for military research and development; the (DIA), responsible for military ; and the National Reconnaissance Office, which designs and maintains reconnaissance for use by the Department of Defense and the intelligence community.The need for the military to consider implications of political,, The Department of Defense is America's largest government agency. Our mission is to provide the military forces needed to deter war and ensure our nation's security., The United States Department of Defense (DoD, [2] USDOD, or DOD) is an executive department of the U.S. federal government charged with coordinating and supervising the six U.S. armed services: the Army, Navy, Marines, Air Force, Space Force, the Coast Guard for some purposes, and related functions and agencies..