United States Department of Defense Department overview Formed September 18, 1947; 70 years ago (1947 - 09 - 18) (as National Military Establishment) Preceding Department U.S. Department of War U.S. Department of the Navy Type Executive Department Headquarters The Pentagon Arlington County, Virginia, US 38 ° 52 ′ 16 '' N 77 ° 3 ′ 21 '' W ﻿ / ﻿ 38.87111 ° N 77.05583 ° W ﻿ / 38.87111; - 77.05583 Coordinates: 38 ° 52 ′ 16 '' N 77 ° 3 ′ 21 '' W ﻿ / ﻿ 38.87111 ° N 77.05583 ° W ﻿ / 38.87111; - 77.05583 Employees 742,000 (civilian) 1,300,000 (active duty military) 826,000 (National Guard and reserve): 2.87 million total (2016) Annual budget US $530.1 billion (2010) US $549.1 billion (2011) US $553.0 billion (est. 2012) US $496.1 billion (2015) US $534.3 billion (base FY2016) Department executives James Mattis, Secretary Patrick M. Shanahan, Deputy Secretary Child agencies U.S. Department of the Army U.S. Department of the Navy U.S. Department of the Air Force Website www.defense.gov
primary military leader within the department of defense
James Mattis, Secretary