The U.S. military has provided support to civil authorities in response to civil emergencies and natural disasters dating back to the Truman era. The terminology applied to this function has varied over the years: military assistance, or military support to civil authorities; military support of civil defense; and employment of military resources in natural disaster emergencies within the United States. As will be illustrated in this report's discussion of U.S. Defense Department (DoD) regulatory documents, the specific responsibilities of the department and the service branches were initially divided between civil defense (attacks on the United States) and disaster-related civil emergencies, but now are addressed collectively as Military Support to Civil Authorities (MSCA) as a matter of departmental policy and doctrine. In addition, the events of September 11, 2001, and the subsequent creation of a homeland security infrastructure have resulted in the adoption of MSCA policy in the context of the broader issue of homeland defense. However, both the core regulations and the DoD internal directive that govern MSCA predate the post-9/11 world, because they were adopted in 1993. In addition, the primary statutory authority for these documents is the Federal Civil Defense Act of 1950, which was repealed in 1994. Consequently, all of the recent policy statements defining MSCA and establishing DoD's role are found in homeland security directives and strategy documents issued by the White House and the military. The U.S. Department of Defense, in its 2005 Strategy for Homeland Defense and Civil Support, defines defense support of civil authorities as "DoD support, including Federal military forces, the Department's career civilian and contractor personnel, and DoD agency and component assets, for domestic emergencies and for designated law enforcement and other activities." This function is provided when DoD is directed to do so by the president or the secretary of defense. A report on the future of the National Guard and Reserves issued in 2006 defines "civil support" as "an umbrella term that encompasses the support the Department of Defense could provide as part of a response to a natural disaster or terrorist attack, to include an event involving chemical, biological, nuclear, radiological, or explosive materials (CBRNE), as well as support DoD could provide for other law enforcement activities." DoD's Homeland Security doctrine issued by the Joint Chiefs of Staff in August 2005 states "MSCA is the most widely recognized form of DOD Civil Support because it usually consists of support for high-profile emergencies such as natural or manmade disasters that often invoke Presidential or state emergency/disaster declarations. DOD assistance should be requested by an LFA (Lead Federal Agency) only when other local, state and federal capabilities have been exhausted or when a military-unique capability is required." MSCA is generally provided during natural disasters, special security events, and accidental or intentional manmade disasters that have evoked a presidential or state emergency declaration. Major Robert Preiss, a former strategic analyst in the National Guard Bureau, defined MSCA in 2003 as "assistance to civilian governmental entities - Federal, state, or local - that the services may provide to help manage a crisis, attack, or calamity." The National Response Plan issued by the Department of Homeland Security in December 2004, which is discussed in greater detail in a separate section of this report, also stipulates that DoD civil support is generally provided only when local, state and other federal resources are "overwhelmed."