Columbia serves as part of the first line of defense for the United States. The state National Guard is organized into units stationed in each of the 50 states, three territories, and the District of Columbia, and operates under their respective state or territorial governor, except in the instance of Washington, D.C., where the National Guard operates under the President of the United States or his designee. The governors exercise control through the state adjutants general. The National Guard may be called up for active duty by the governors to help respond to domestic emergencies and disasters, such as hurricanes, floods, and earthquakes. National Guard Bureau The National Guard is administered by the National Guard Bureau, which is a joint activity of the Army and Air Force under the DoD. The National Guard Bureau provides a communication channel for state National Guards to the DoD. The National Guard Bureau also provides policies and requirements for training and funds for state Army National Guard and state Air National Guard units, the allocation of federal funds to the Army National Guard and the Air National Guard, and other administrative responsibilities prescribed under . The National Guard Bureau is headed by the Chief of the National Guard Bureau (CNGB), who is a four-star general in the Army or Air Force and is a member of the Joint Chiefs of Staff. The National Guard Bureau is headquartered in Arlington County, Virginia, and is a joint activity of the Department of Defense to conduct all the administrative matters pertaining to the Army National Guard and the Air National Guard. The chief is either an Army or an Air Force four-star general officer, and is the senior uniformed National Guard officer, and is a member of the Joint Chiefs of Staff. In this capacity, he serves as a military adviser to the President, the Secretary of Defense, the National Security Council and is the Department of Defense's official channel of communication to the Governors and to State Adjutants General on all matters pertaining to the National Guard. He is responsible for ensuring that the more than half a million Army and Air National Guard personnel are accessible, capable, and ready to protect the homeland and to provide combat resources to the Army and the Air Force. He is appointed by the President in his capacity as Commander in Chief. Constitutional basis The respective state National Guards