Department of Defense

• Establishment: The United States Department of Defense (DoD) was established on September 18, 1947, following the National Security Act of 1947, which unified the military departments under a single executive department. • Pentagon Headquarters: The DoD is headquartered in the Pentagon, one of the world’s largest office buildings, which has over 17 miles of corridors and houses approximately 23,000 employees. • Largest Employer: The Department of Defense is the world’s single largest employer, with over 2.8 million service members and civilian employees. • Origin of the Name: The name "Department of Defense" replaced "National Military Establishment" in 1949 to reflect the department’s broader mission beyond just military operations. • Unified Command Structure: The DoD oversees the Joint Chiefs of Staff and unified combatant commands, ensuring coordination among the Army, Navy, Air Force, Marine Corps, and Space Force. • Space Force Addition: The newest military branch, the U.S. Space Force, was established within the Department of the Air Force in December 2019, and falls under the DoD. • Defense Budget: The DoD has the largest discretionary budget of any U.S. federal agency, with annual budgets exceeding $800 billion in recent years. • Global Presence: The DoD maintains over 800 military bases in more than 70 countries worldwide, ensuring a global U.S. military presence. • Historical Integration: President Harry S. Truman signed an Executive Order in 1948 desegregating the U.S. Armed Forces, making the DoD a key player in civil rights progress. • 9/11 Attack: On September 11, 2001, the Pentagon was struck by American Airlines Flight 77, killing 125 people in the building and 59 passengers and crew, marking the deadliest attack on the DoD headquarters in history.