United States Department of Defense

Department of Defense
Learn about the Department of Defense and The Pentagon building

What is the United States Department of Defense?

The United States Department of Defense (DOD, sometimes written as DoD) is the federal department responsible for coordinating and supervising all government agencies and functions relating directly to national security and the military. The organization and functions of the Department of Defense are outlined in Title 10 of the United States Code.

The Department of Defense (DoD) is an executive branch of the United States government responsible for coordinating and supervising all government agencies and functions relating directly to national security and the armed forces. Its primary mission is to protect and defend the United States and its interests.

The DOD plays a crucial role in the United States’ national security. It is responsible for three main priorities:

  • Maintaining military readiness
  • Deterring potential adversaries
  • Defending the nation against external threats

Also, the department supports civil authorities in domestic disaster response. In addition, it provides humanitarian assistance in times of crisis.

When was it established?

The Department of Defense was established on September 18, 1947. It is headquartered at the Pentagon in Arlington, Virginia. It is led by the Secretary of Defense, a civilian appointed by the President and confirmed by the Senate. The Secretary of Defense is responsible for formulating defense policy, overseeing military operations, and managing the various military departments and agencies.

DOD Departments

The DoD has several major components, including the military departments: the Army, Navy, Air Force, and Marine Corps. Each military department is headed by a civilian Secretary who reports to the Secretary of Defense. These departments are responsible for the recruitment, training, equipping, and readiness of their respective military services.

In addition to the military departments, the DoD includes several defense agencies and combatant commands. Defense agencies, such as the Defense Intelligence Agency (DIA) and the Defense Logistics Agency (DLA), provide specialized services and support to the military. Combatant commands, such as the U.S. Central Command (CENTCOM) and U.S. European Command (EUCOM), have geographic or functional responsibilities for military operations in specific world regions.

The DoD collaborates closely with intelligence agencies, international partners, and other government departments to ensure effective defense and security strategies. It conducts research and development to advance military capabilities and technologies and engages in diplomatic efforts to promote peace and stability.

Budget and Funding

The DoD has budget is one of the largest in the federal government. The budget accounts for a significant portion of the overall federal discretionary spending. The budget allocates funds for:

  • Department personnel
  • Operations and facility maintenance
  • Research and development (R&D)
  • Procurement of equipment and weapons systems
  • Other defense-related activities.

Overall, the Department of Defense is a vital institution that safeguards the nation and its interests, ensuring the security of the United States at home and abroad.

Among the many Department of Defense agencies are:

  • The Missile Defense Agency
  • The Defense Advanced Research Projects Agency (DARPA)
  • The Pentagon Force Protection Agency (PFPA)
  • The Defense Intelligence Agency (DIA)
  • The National Geospatial-Intelligence Agency (NGA)
  • The National Security Agency (NSA)

Training Academies

The department operates several joint service schools and training academies, including the National War College. For example, the following are military training academies sponsored by the DOD:

  • Air Force Academy (Colorado Springs, Colorado)
  • Coast Guard Academy (New London, Connecticut)
  • Merchant Marine Academy (Kings Point, N.Y.)
  • Military Academy (West Point, N.Y.) – Provides education and training for the U.S. Army.
  • Naval Academy (Annapolis, Maryland) – The undergraduate college of the United States Navy that trains men and women to become professional Navy officers.

The Pentagon: The United States Department of Defense Headquarters

The Pentagon is the headquarters of the United States Department of Defense and is located in Arlington, Virginia. “The Pentagon” refers to the Department of Defense rather than the building itself.

American architect George Bergstrom (1876 – 1955) designed the building. John McShain, a Philadelphia general contractor, built the facility. Construction began on September 11, 1941. The finished Pentagon facility was dedicated on January 15, 1943.

The Department of Defense is the primary tenant of The Pentagon building near Washington, D.C., and has three major components: The Department of the Army, The Department of the Navy, and the Department of the Air Force.

The Pentagon Reservation

The Pentagon Reservation is located in southeastern Arlington County, Virginia. It is between a large man-made lagoon (the Lagoon, formed during construction) and the southeastern corner of Arlington National Cemetery. The northeastern and eastern facades have unobstructed views of the Monumental Core of the Nation’s Capital across the Potomac River.

Also, The Pentagon’s relatively low profile permits clear vistas of Washington from the highlands of Arlington National Cemetery. The Pentagon is the world’s largest office building by floor area. It has about 6,500,000 square feet, of which 3,700,000 square feet is office space. In comparison, the Pentagon building is twice the size of the Merchandise Mart in Chicago, Illinois. Also, it has three times the floor space of the Empire State Building in New York.

The U.S. National Capitol could fit into the building’s five wedge-shaped sections. Approximately 23,000 military and civilian employees and about 3,000 non-defense support personnel work in the Pentagon. The Pentagon has five sides. Five floors are above ground (plus two basement levels below ground), and five ring corridors per floor have 17.5 miles of corridors.

The building includes a five-acre central plaza shaped like a pentagon. The central plaza is informally known as “ground zero,” a nickname originating during the Cold War and based on the presumption that the Soviet Union would target one or more nuclear missiles at this central location in the outbreak of a nuclear war.

The Pentagon Official Website – Provides information on the Pentagon, its history, tour booking information, facts and figures, and more.

What does a Private Investigator need to know about the Department of Defense?

A private investigator (PI) may need to be aware of certain aspects of the Department of Defense (DoD) if their investigations involve matters that intersect with military or defense-related issues. Here are some key points that a private investigator might need to know:

Security Clearance Levels: Understanding the various levels of security clearance within the Department of Defense can be crucial. Information at higher clearance levels is more restricted, and access to such information may be limited.

Military Regulations and Procedures: Familiarity with military regulations and procedures is important, as these can impact investigations involving military personnel or facilities. This includes knowledge of the Uniform Code of Military Justice (UCMJ) and other relevant regulations.

Military Bases and Installations: Knowledge of military bases and installations is essential if the investigation involves activities or individuals associated with these locations. Access restrictions and the presence of military police may affect the investigator’s ability to gather information.

Personnel Records and Military ID Verification: Verifying military service and obtaining personnel records may be necessary for certain investigations. Understanding how to request and navigate military records is important.

Military Courts and Legal Processes: A private investigator should be aware of military courts and legal processes if the investigation involves legal matters related to military personnel. Military legal systems operate differently from civilian ones.

Defense Contractors and Contracts: Investigations involving defense contractors or contracts may require understanding the procurement processes, defense industry practices, and relevant regulations governing defense contracts.

Veterans Affairs (VA) Records: In cases where veterans are involved, knowledge of VA records and benefits may be important. This can include understanding the types of information available and the processes for obtaining it.

Cybersecurity and Information Protection: Given the sensitive nature of defense-related information, investigators should be cautious about handling and protecting any information obtained during their work to avoid legal repercussions.

Interagency Collaboration: In certain cases, collaboration with law enforcement agencies or government entities may be necessary. Understanding how to navigate collaborations with military or defense-related agencies is crucial.

Understanding Military Culture: A basic understanding of military culture can be beneficial for interacting with military personnel and gaining their trust. This includes knowledge of rank structures, customs, and traditions.

It’s important to note that private investigators must operate within the bounds of the law, and there are specific legal and ethical considerations when dealing with sensitive information related to national security. If an investigation involves classified information or activities, it is imperative to consult with legal professionals and comply with all relevant laws and regulations.

To learn more, visit the official Department of Defense website. The website includes the latest news and issues the department is dealing with. Provides a list of all DOD sites and other resources.

Learn about other government intelligence agencies.

Michael Kissiah is the owner of Brandy Lane Publishing, LLC, which owns and operates a small portfolio of websites, including eInvestigator.com. Michael created eInvestigator.com more than 20 years ago after working as a private investigator in the state of Florida. Since that time, he has become an expert at how to find information online and has written over 1000 articles on topics related to the investigation industry. In addition, he is the author of the "Private Investigator Licensing Handbook", available at Amazon.com.


  1. I cannot find an email address for the Sec. of Defense, James Mattis. I have a question for him. Yesterday, President Trump said the US would soon withdraw troops from Syria. At present, there are at least 2000 occupying space in Syria along with SDF troops funded by the US. Their spokesperson followed up the Trump statement saying they have no word of the proposed change. Who is lying, Truimp or the SDF spokesperson? Secy. Mattis can kindly answer that, Or, does his silence mean that he doesn’t know who is the liar. To me, a US citizen and Korean War vet it seems that there is still a US goal of regime change in Syria. If so, why?


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