As a rule, DoD intervention comes “in response to a request for assistance from civil authorities for domestic emergencies, law enforcement agency support, and other domestic activities. The most visible support is provided during major natural and man-made disasters and other incidents.”
Except in cases of imminent loss of life or similar extremes, requests for military assistance are supposed to undergo a threshold review to establish their legality.
“A key factor in determining whether DoD should provide support of non-DoD entities is identifying the authority that directs or allows the support. U.S. law, Presidential Executive Orders and directives, federal regulations, and DoD policies provide the framework and authorities for DoD to provide support of non-DoD entities…. Responsibilities also may be reflected in memorandums of agreement (MOAs).”
The new DoD manual details the elements of that legal and regulatory framework. It identifies the six standing Execute Orders (EXORDs) that authorize DoD support to civilian authorities, the relevant presidential directives, and the array of other instructions, regulations, statutes and directives that constrain or empower the U.S. military in domestic civilian matters.
The manual addresses DoD rules for the use of force (RUF), and describes a wide range of potential DoD missions in the civilian arena, including: search and rescue, explosive ordnance disposal, response to chemical, biological, radiological or nuclear incidents, pandemics, acts of terrorism, mass migration emergencies, and civil disturbances, as well as support to National Special Security Events and to national and international sporting events, among other missions.
See DoD Manual 3025.01, Volume 1 – Defense Support of Civil Authorities: Overview, August 11, 2016
DoD Manual 3025.01, Volume 2 – Defense Support of Civil Authorities: Incident Response, August 11, 2016
DoD Manual 3025.01, Volume 3 – Defense Support of Civil Authorities: Pre-Planned DoD Support of Law Enforcement Agencies, Special Events, Community Engagement, and Other Non-DoD Entities, August 11, 2016