- The United States Department of Defense (DoD, USDOD, or DOD) is an executive branch department of the federal government of the United States charged with coordinating and supervising all agencies and functions of the U.S. government directly related to national security and the United States Armed Forces. As of November 2022, the U.S. Department of Defense is the second largest employer in the world—After India; and potentially China, if including the Central Military Commission. With over 1.4 million active-duty service personnel, including soldiers, marines, sailors, airmen, and guardians. The Department of Defense also maintains over 778,000 National Guard and reservists, and over 747,000 civilians bringing the total to over 2.91 million employees. Headquartered at the Pentagon in Arlington County, Virginia, just outside Washington, D.C., the Department of Defense’s stated mission is “to provide the military forces needed to deter war and ensure our nation’s security”.