JP 3-28, page 26

Chapter I I-4 JP 3-28 3. Homeland Security, Homeland Defense, and Defense Support of Civil Authorities The terms homeland security (HS), HD, and DSCA are distinct operations. a. HS is a concerted national effort to prevent terrorist attacks within the US; reduce America’s vulnerability to terrorism, major disasters, and other emergencies; and minimize the damage and recover from attacks, major disasters, and other emergencies that occur. HS is an integral element of a broader US national security and domestic policy. Protecting the US from terrorism is the cornerstone of HS. (1) HS describes the intersection of evolving threats and hazards with traditional governmental and civic responsibilities for civil defense, emergency response, law enforcement, customs, border control, and immigration (see Figure I-1). DSCA [Defense Support of Civil Authorities]. Support provided by US federal military forces, DOD [Department of Defense] civilians, DOD contract personnel, DOD component assets, and National Guard forces (when the Secretary of Defense, in coordination with the Governors of the affected States, elects and requests to use those forces in Title 32, US Code, status) in response to requests for assistance from civil authorities for domestic emergencies, law enforcement support, and other domestic activities, or from qualifying entities for special events. Emergency authority. A federal military commander’s authority, in extraordinary emergency circumstances where prior authorization by the President is impossible and duly constituted local authorities are unable to control the situation, to engage temporarily in activities that are necessary to quell large-scale, unexpected civil disturbances because (1) such activities are necessary to prevent significant loss of life or wanton destruction of property and are necessary to restore governmental function and public order or (2) duly constituted federal, state, or local authorities are unable or decline to provide adequate protection for federal property or Federal governmental functions. Immediate response authority. A federal military commander's, DOD component head’s, and/or responsible DOD civilian official’s authority temporarily to employ resources under their control, subject to any supplemental direction provided by higher headquarters, and provide those resources to save lives, prevent human suffering, or mitigate great property damage in response to a request for assistance from a civil authority, under imminently serious conditions when time does not permit approval from a higher authority within the United States. Immediate response authority does not permit actions that would subject civilians to the use of military power that is regulatory, prescriptive, proscriptive, or compulsory. Source: Adopted from Department of Defense Directive 3025.18, Defense Support of Civil Authorities (DSCA)