The United States Department of Defense (DoD,[2] USDOD, or DOD) is an executive branch department of the federal government of the United States charged with coordinating and supervising the five U.S. armed services, the Army; Navy; Marines; Air Force; Space Force; the Coast Guard for some purposes, and related functions and agencies.

[1] 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".

Upon the seating of the 1st U.S. Congress on March 4, 1789, legislation to create a military defense force stagnated as they focused on other concerns relevant to setting up the new government.

After the end of World War II, President Harry Truman proposed the creation of a unified department of national defense.

In a special message to the Congress on December 19, 1945, the president cited wasteful military spending and interdepartmental conflicts.

[12][13][14] The National Military Establishment formally began operations on September 18, the day after the Senate confirmed James V. Forrestal as the first secretary of defense.

The Act clarified the overall decision-making authority of the secretary of defense concerning these subordinate military departments.

OSD is the principal staff element of the Secretary of Defense in the exercise of policy development, planning, resource management, fiscal and program evaluation and oversight, and interface and exchange with other U.S. federal government departments and agencies, foreign governments, and international organizations, through formal and informal processes.

They fulfill the requirements of national policymakers and war planners, serve as Combat Support Agencies, and also assist and deploy alongside non-Department of Defense intelligence or law enforcement services such as the Central Intelligence Agency and the Federal Bureau of Investigation.

[21][22][23][24] Following the Goldwater–Nichols Act in 1986, the Joint Chiefs of Staff no longer maintained operational command authority individually or collectively.

They have the legal authority under Title 10 of the United States Code to conduct all the affairs of their respective departments within which the military services are organized.

"[31] The Defense Reorganization Act of 1958 removed the power of command over troops from secretaries of military departments and service chiefs.

[31] As of 2019[update], the United States has eleven Combatant Commands, organized either on a geographical basis (known as "area of responsibility", AOR) or on a global, functional basis:[33] Department of Defense spending in 2017 was 3.15% of GDP and accounted for about 38% of the budgeted global military spending – more than the next 7 largest militaries combined.

[38] The subsequent 2010 Department of Defense Financial Report shows the total budgetary resources for fiscal year 2010 were $1.2 trillion.

The FY2019 Budget for the Department of Defense is approximately $686,074,048,000[44] (Including Base + Overseas Contingency Operations + Emergency Funds) in discretionary spending and $8,992,000,000 in mandatory spending totaling $695,066,000,000 Undersecretary of Defense (Comptroller) David L. Norquist said in a hearing regarding the FY 2019 budget: "The overall number you often hear is $716 billion.

[46] The Department of Defense is unique because it is one of the few federal entities where the majority of its funding falls into the discretionary category.

* Numbers may not add due to rounding As of 10 March 2023 the fiscal year 2024 (FY2024) presidential budget request was $842 billion.

[66][67] A 2013 Reuters investigation concluded that Defense Finance & Accounting Service, the Department of Defense's primary financial management arm, implements monthly "unsubstantiated change actions"—illegal, inaccurate "plugs"—that forcibly make DoD's books match Treasury's books.

In 2016, The Washington Post uncovered that rather than taking the advice of the auditing firm, senior defense officials suppressed and hid the report from the public to avoid political scrutiny.

[71] In June 2016, the Office of the Inspector General released a report stating that the Army made $6.5 trillion in wrongful adjustments to its accounting entries in 2015.

[73] In the latest Center for Effective Government analysis of 15 federal agencies which receive the most Freedom of Information Act requests, published in 2015 (using 2012 and 2013 data, the most recent years available), the DoD earned 61 out of a possible 100 points, a D− grade.

In January 2025, the Department of Defense announced that it would introduce an annual "rotation program" for media at the Pentagon, starting February 14, 2025.

Established media outlets including the New York Times, NBC News, National Public Radio (NPR) and Politico will have to vacate their workspaces, some of which they have occupied for decades.

[76][77] Barbara Starr mentioned in the Columbia Journalism Review, that for now "at least", several institutions remain, including CBS, CNN, ABC, Reuters, and the Associated Press.