United States Department of Defense United States Department of Defense The Department of Defense (DoD, USDOD, or DOD) is an executive branch department of the federal government charged with coordinating and supervising all agencies and functions of the government concerned directly with national security and the United States Armed Forces. The department is the largest employer in the world, with nearly 1.3 million active duty servicemen and women as of 2016. Adding to its employees are over 826,000 National Guardsmen and Reservists from the four services, and over 742,000 civilians bringing the total to over 2.8 million employees. Headquartered at the Pentagon in Arlington, Virginia,
Arlington County, Virginia in the county, while 86% commute in, with 27% commuting from Fairfax County. An additional 92,784 people commute out for work, with 42% commuting to DC, and 29% commuting to Fairfax County. A number of federal agencies are headquartered in Arlington, including the Air Force Office of Scientific Research, American Battle Monuments Commission, DARPA, Diplomatic Security Service, Drug Enforcement Administration, Foreign Service Institute, the DHS National Protection and Programs Directorate, Office of Naval Research, Transportation Security Administration, United States Department of Defense, United States Marshals Service, and the United States Trade and Development Agency. Companies headquartered in Arlington include AES,