The United States Department of Defense (DoD) is an executive department of the U.S. federal government charged with coordinating and supervising the U.S. Armed Forces. Headquartered at the Pentagon in Arlington County, Virginia, just outside Washington, D.C., the Department of Defense’s mission is “to provide the military forces needed to deter war and ensure our nation’s security.” Armed Forces under the purview of DoD include the Army, Navy, Marines, Air Force, Space Force, and the Coast Guard (under the Navy Department) during times of war. In 2003 the Department of Homeland Security took over administrative control over the Coast Guard during times of peace.

U.S. Navy

The Navy, likewise founded in 1775, is regarded as the primary maritime defense force. The Navy is also a main supporter of the Air Force in providing air force carriers for transporting aircraft and a runway at sea for aircraft. The purpose of the U.S. Navy is to maintain combat-ready naval forces to deter aggression, ensure freedom of the seas, and project power globally, thereby protecting American interests, preserving economic prosperity, and supporting national security goals through both diplomatic and decisive combat operations. Its mission statement includes defending the nation from attack, maintaining a strategic global influence, and enabling peaceful resolution of crises through its global naval presence.

U.S. Marine Corps

The Marine Corps is the second smallest branch of the military. When it was first established in 1775, it was under the Navy as a ground force enforcement of the branch. It was basically assigned the task of taking over the beaches when the Navy brought them into a mission. In 1798, it was established as a separate branch and since that time has slowly moved more towards ground force operations. The purpose of the U.S. Marine Corps is to be the nation’s naval expeditionary force in readiness, providing innovative, agile, and versatile warfighting capabilities across land, air, and sea domains to project power and respond rapidly to global threats. Its mission is to protect the United States, conducting humanitarian operations, and securing naval bases and U.S. embassies worldwide.

U.S. Air Force

The Air Force is the most recently established branch and was officially established as a separate branch in 1947. Its main purpose is to support the security of the U.S. through air and space exploitation. It is a main supporter of ground forces by providing air support and cyber capabilities during missions, enabling the nation to achieve global vigilance, global reach, and global power. Its mission is to fly, fight, and win airpower anytime, anywhere, by achieving air superiority, providing global strike capabilities, ensuring rapid global mobility, conducting intelligence, surveillance, and reconnaissance (ISR), and establishing command and control.

U.S. Coast Guard

The Coast Guard was originally established in 1790 and has undergone several changes, now falling under the jurisdiction of the Department of Homeland Security. The purpose of the U.S. Coast Guard is to ensure the safety, security, and environmental stewardship of the nation’s waters. Its mission encompasses protecting the U.S. border and waterways, responding to maritime emergencies, conducting maritime law enforcement, and executing defense operations.

National Guard

The National Guard is a state-based military force that becomes part of the U.S. military’s reserve components of the U.S. Army and the U.S. Air Force when activated for federal missions. It is a military reserve force composed of National Guard military members or units of each state, the territories of Guam, the U.S. Virgin Islands, Puerto Rico, and the District of Columbia, for a total of 54 separate organizations. It is officially created under Congress’s Article I, Section 8 enumerated power to “raise and support Armies.” All members of the National Guard are also members of the organized militia of the United States. National Guard units are under the dual control of U.S. state governments and the U.S. federal government. Colonial militias were formed during the British colonization of the Americas from the 17th century onward. The first colony-wide militia was formed by Massachusetts in 1636 by merging small, older local units. The various colonial militias became state militias when the United States became independent. The title “National Guard” was used in 1824 by some New York State militia units, named after the French National Guard in honor of the Marquis de Lafayette. “National Guard” became a standard nationwide militia title in 1903 and has specifically indicated reserve forces under mixed state and federal control since 1933.