United States Department of Defense

The Department of Defense, also known as the Department of the United States or simply the DoD, is a cabinet-level department of the United States federal government that is responsible for coordinating and supervising all other government agencies and functions that are directly related to matters of national security and the United States Armed Forces. As of the year 2021, the Department of Defense (DoD) had more over 1.4 million active-duty military personnel, which included soldiers, marines, sailors, airmen, and guardians. To bring the overall number of employees up to over 2.8 million, additional workers include more than 826,000 members of the National Guard and reservists from the armed services, as well as more than 732,000 civilians. The Department of Defense (DoD) has the objective of providing "the military forces required to prevent conflict and guarantee the security of our country." The DoD's headquarters are located in Arlington, Virginia, just outside of Washington, District of Columbia.

The Secretary of Defense is a cabinet-level position that reports directly to the President of the United States of America. This position oversees all aspects of the Department of Defense. The Department of the Army, the Department of the Navy, and the Department of the Air Force are the three military departments that are subordinate to the Department of Defense. In addition, the Department of Defense is in charge of four of the nation's intelligence agencies, which are the National Security Agency (NSA), the National Geospatial-Intelligence Agency (NGA), the National Reconnaissance Office (NRO), and the Defense Intelligence Agency (DIA) (NRO). Other agencies that fall under the purview of the Secretary of Defense include the Defense Advanced Research Projects Agency (DARPA), the Defense Logistics Agency (DLA), the Missile Defense Agency (MDA), the Defense Health Agency (DHA), the Defense Threat Reduction Agency (DTRA), the Defense Counterintelligence and Security Agency (DCSA), the Space Development Agency (SDA), and the Pentagon Force Protection Agency (PFPA). In addition, the Department of Defense is accountable for the administration of contracts via the Defense Contract Management Agency, sometimes known as DCMA. There are eleven regional or functional Unified combatant commands that are responsible for managing military activities. In addition, the Department of Defense oversees the operation of a number of joint services institutions, such as the National War College and the Eisenhower School (ES) (NWC).