United States National Guard in the context of "Active Guard Reserve"

The United States Army Corps of Engineers (USACE) is the military engineering branch of the United States Army. A direct reporting unit (DRU), it has three primary mission areas: Engineer Regiment, military construction, and civil works. USACE has 37,000 civilian and military personnel, making it one of the world's largest public engineering, design, and construction management agencies. The USACE workforce is approximately 97% civilian, 3% active duty military. The civilian workforce is mainly located in the United States, Europe and in select Middle East office locations. Civilians do not function as active duty military and are not required to be in active war and combat zones; however, volunteer (with pay) opportunities do exist for civilians to do so.

The day-to-day activities of the three mission areas are administered by a lieutenant general known as the chief of engineers/commanding general. The chief of engineers commands the Engineer Regiment, comprising combat engineer, rescue, construction, dive, and other specialty units, and answers directly to the chief of staff of the Army. Combat engineers, sometimes called sappers, form an integral part of the Army's combined arms team and are found in all Army service components: Regular Army, National Guard, and Army Reserve. Their duties are to breach obstacles; construct fighting positions, fixed/floating bridges, and obstacles and defensive positions; place and detonate explosives; conduct route clearance operations; emplace and detect landmines; and fight as provisional infantry when required. For the military construction mission, the chief of engineers is directed and supervised by the Assistant Secretary of the Army for installations, environment, and energy, whom the President appoints and the Senate confirms. Military construction relates to construction on military bases and worldwide installations.

Title 32 of the United States Code outlines the role of the United States National Guard in the United States Code. It is one of two ways the National Guard can be activated by the US Federal Government. Under Title 32, National Guard remains under control of the state but is funded by the federal government. Under Title 10, the National Guard can be commanded by the President of the United States under certain conditions.

• 32 U.S.C. ch. 1—Organization
• 32 U.S.C. ch. 3—Personnel
• 32 U.S.C. ch. 5—Training
• 32 U.S.C. ch. 7—Service, Supply, And Procurement
• 32 U.S.C. ch. 9—Homeland Defense Activities

The Puerto Rico National Guard (PRNG; Spanish: Guardia Nacional de Puerto Rico) is the national guard of the U.S. Commonwealth of Puerto Rico. The Constitution of the United States specifically charges the National Guard with dual federal and state missions, which includes to provide soldiers and airmen to the United States Army and U.S. Air Force in national emergencies or when requested by the president of the United States, and to perform military operations at the state level or any other lawful service as requested by the governor of Puerto Rico. The PRNG responds to the governor of Puerto Rico, who serves as its commander in chief and imparts orders with the Puerto Rico adjutant general acting as conduit, and its local mission is to respond as requested in military or civilian tasks. Abroad, its main function is to train a reserve capable of providing additional personnel in a war scenario.

The District of Columbia National Guard is the branch of the National Guard of the United States based in the District of Columbia. It comprises both the D.C. Army National Guard and the D.C. Air National Guard components.

The president of the United States is the commander-in-chief of the District of Columbia National Guard. Command is exercised through the secretary of defense and the commanding general, Joint Force Headquarters (JFHQ), District of Columbia National Guard. In 1949, President Truman issued Executive Order No. 10030, of January 26, 1949, providing authority for the Secretary of Defense to delegate his command authority over the D.C. National Guard to: the secretary of the Army for the D.C. Army National Guard, and the secretary of the Air Force for the D.C. Air National Guard. However, in 1969, President Nixon issued Executive Order 11485, revoking the previous authorities of EO 10030. The secretary of defense then delegated command authority to the Secretary of the Army, operating through the singular commanding general of the D.C. National Guard. In 2021, the secretary of defense amended the previous delegation of authority to the secretary of the Army, to explicitly specify a single point of contact, the DoD executive secretary, for all requests from or for assistance by the D.C. National Guard. Further, the secretary of defense retained sole authority over such requests when actions within 48 hours are required, or if the anticipated request will include support of civilian law enforcement, such as “crowd control, traffic control, search, seizure, arrest, or temporary detention.”

The Illinois National Guard comprises both Army National Guard and Air National Guard components of Illinois. As of 2013, the Illinois National Guard has approximately 13,200 members. The National Guard is the only United States military force empowered to function in a state status. The Constitution of the United States specifically charges the National Guard with dual federal and state missions. Those functions range from limited actions during non-emergency situations to full scale law enforcement of martial law when local law enforcement officials can no longer maintain civil control. The National Guard may be called into federal service in response to a call by the President or Congress.

The Insurrection Act of 1807 is the U.S. federal law that empowers the president of the United States to nationally deploy the U.S. military and to federalize the National Guard units of the individual states in specific circumstances, such as the suppression of civil disorder, of insurrection, and of armed rebellion against the federal government of the U.S. The Insurrection Act provides a statutory exception to the Posse Comitatus Act (1878) that limits the president's deploying the U.S. military to enforce either civil law or criminal law within the United States.

After invoking and before exercising the powers authorized under the Insurrection Act, Title 10 U.S.C. § 254 requires the publication of a presidential proclamation whereby the U.S. President formally orders the dispersion of the peoples committing civil unrest or armed rebellion. The Defense Department guidelines define "homeland defense" as a constitutional exception to the restrictions of the Posse Comitatus Act; therefore, the political, military, and police measures necessary to protect national security from external threats are exceptions to the restrictions of the act.