10 U.S.C. § 274 — Maintenance and operation of equipment

(a) The Secretary of Defense may, following other applicable laws, make Department of Defense personnel available to maintain equipment for federal, state, and local civilian law enforcement, including equipment supplied under section 3721 of this title. (b) (1) On top of maintenance, and subject to paragraph (2), the Secretary may — if a federal law enforcement agency asks — make Defense personnel available to operate equipment for: a criminal violation of the laws listed in paragraph (4)(A); assistance the agency is allowed to give a state, local, or foreign government enforcing similar laws; a domestic or foreign counter-terrorism operation; or bringing a suspected terrorist from a foreign country to stand trial in the U.S. (2) Defense personnel lent to a civilian agency under this subsection may only operate equipment for: (A) detecting, tracking, and communicating the movement of air and sea traffic; (B) detecting, tracking, and communicating surface traffic movement outside the U.S., and within the U.S. up to 25 miles of the border if detection started outside it; (C) aerial reconnaissance; (D) intercepting vessels or aircraft detected outside U.S. land to direct them to a location civilian officials designate; (E) operating equipment to support communications for the law enforcement programs listed in (4)(A); and (F) — only with joint approval of the Secretary of Defense and the Attorney General (and the Secretary of State for operations outside the U.S.) — transporting civilian law enforcement and supporting personnel on a joint operation, running a base of operations for them, and transporting suspected terrorists to the U.S. for trial, as long as the requesting agency provides all the security and keeps custody the whole time. (3) Personnel operating equipment for the purpose in (2)(D) may keep operating it into U.S. land when chasing a vessel or aircraft first detected outside U.S. land. (4) In this subsection: (A) "Federal law enforcement agency" means a federal agency that enforces the Controlled Substances Act, the Controlled Substances Import and Export Act, sections 274 through 278 of the Immigration and Nationality Act, tariff and customs laws on merchandise entering or leaving U.S. customs territory or other U.S. territory, chapter 705 of title 46, or any law against terrorism. (B) "Land area of the United States" includes the land of any U.S. territory, commonwealth, or possession. (c) For any other purpose besides those listed in (b)(2), the Secretary may still make Defense personnel available to operate equipment for civilian law enforcement, following other applicable laws — but only to the extent this support doesn't count as direct participation by those personnel in a civilian law enforcement operation, unless direct participation is separately authorized by law.