The U.S. Department of the Army is one of the armed forces service departments in the United States Department of Defense. It is headed by the secretary of the army, who is responsible for the administrative affairs of the U.S. Army. Based in Washington, D.C., the department has a large collection of military weapons, including individual and crew-served weapons and equipment, aircrafts, air defense artillery, antiarmor weapons, indirect fire systems, tracked and wheeled vehicles, and nuclear, biological and chemical defense equipment. It is a part of the Department of Defense, which offers a wide range of services, including war fighting, humanitarian aid, peacekeeping, disaster relief and homeland security.