JP 3-28, page 61

Supporting Civilian Law Enforcement Agencies III-5 (5) Operation of equipment to facilitate communications in connection with law enforcement programs specified in Title 10, USC, Section 274(b). (6) DOD personnel may also be made available to operate equipment for the following additional purposes subject to joint approval by SecDef and the Attorney General (and the Secretary of State in the case of a law enforcement operation outside of the land area of the US). (a) Transportation of civilian law enforcement personnel along with any other civilian or military personnel who are supporting or conducting a joint operation with civilian law enforcement personnel. (b) Operation of a base of operations for civilian law enforcement and support personnel. (c) Transportation of suspected terrorists from foreign countries to the US for trial (so long as the requesting federal LEA provides all security for such transportation and maintains custody of the suspect through the duration of the transportation). e. Other Permissible Assistance. Under Title 10, USC, Section 271, the transfer of information acquired in the normal course of military operations to civilian LEAs is not a violation of the PCA. Additionally, DODI 3025.21, Defense Support of Civilian Law Enforcement Agencies, provides that other actions that are approved by the Secretaries of the Military Departments or the directors of the DOD agencies that do not subject civilians to the regulatory, prescriptive, proscriptive, or compulsory use of military power are not a violation of the PCA. (1) Border Security and Immigration Enforcement Support. DOD provides support to other federal agencies in border security and in the event of a mass migration emergency. Historically, this law enforcement support is in the form of technical assistance, services, and facilities and only on a temporary basis. GCCs can expect to be designated as the supported commander for support to DHS in mass migration operations. CDRUSNORTHCOM should expect to be designated as the supported commander for limited support to DHS collection relocation processing centers on DOD installations in CONUS. US Southern Command can be expected to be designated as the supported command for temporary mass migration operations at Guantanamo Bay, Cuba. (2) Counterterrorism Operations. The US Attorney General, acting through the FBI and in cooperation with the heads of other federal departments, agencies, and military criminal investigative organizations (MCIOs), coordinates domestic intelligence collection and the activities of the law enforcement community to prevent, protect against, mitigate, respond to, and recover from terrorist attacks and to identify the perpetrators and bring them to justice in the event of a terrorist incident. (a) If there is a credible threat, DOD may also be requested to support LEAs with the pre-positioning of forces. NG reaction forces can also be requested to support counterterrorism operations. In the case of an imminent threat to life or severe property