Recently I saw an action movie about military police officer in the U.S. One question surfaced for me - as far as I understand main task of military police (including its investigators) is to combat crime inside U.S. army (and crime related to the army). On the other hand, as far as I remember almost in every country, including U.S., army cannot be used on the domestic territory for pretty much any operations. As I understand, military police is part of the military and technically any investigation or operation which military police will perform would be a violation of this ban on usage of army in homeland.

How this paradox is resolved from legal perspective? Am I misunderstanding something?

  • Exactly what is this "paradox" you see? The military police (MPs) only investigate crimes by the military, on and off military bases. The MPs are not the military as a whole. How are the MP's "used on the domestic territory for pretty much any operations"? Read law.stackexchange.com/questions/14813/… Commented Feb 15, 2018 at 17:01
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    The Posse Comitatus Act generally forbids the military from enforcing civilian law. But members of the military are bound by military law (look up the UCMJ) and the military police, military courts, etc, are perfectly free to enforce military law wherever it applies. There is no general prohibition against the military operating within the US; they can do more or less anything else (train, supply, build dams, assist with natural disasters, operate missile silos, whatever) as long as they don't attempt to enforce civilian law. Commented Feb 15, 2018 at 17:15
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    @Nate Eldredge that looks an awful lot like an answer.
    – Stackstuck
    Commented Feb 15, 2018 at 18:01
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    @NateEldredge The military can especially operate on domestic soil for the purpose of fighting military invasions.
    – phoog
    Commented Feb 15, 2018 at 19:24

1 Answer 1


It's probably not a good idea to take action movies as authoritative sources on the law. The law that you're referring to is presumably the Posse Comitatus Act (18 USC 1385) which says

Whoever, except in cases and under circumstances expressly authorized by the Constitution or Act of Congress, willfully uses any part of the Army or the Air Force as a posse comitatus or otherwise to execute the laws shall be fined under this title or imprisoned not more than two years, or both.

There is an article on the act which reviews the pre-history of the act and subsequent congressional authorizations, and there have been many, e.g. the Rivers and Harbors Act of 1894, Espionage Act of 1917, 33 USC 3 pertaining to gunnery ranges, Fisheries and Conservation Management Act of 1976 and so on. The military police are authorized to enforce military law (though not civilian law), see article 7 of the UCMJ, authorized by Congress in Title 10.

P. 167 of the article discusses limits on arrest and investigative powers: their powers pertain almost exclusively to the military.

  • Yes, it's simple. US Military Police are "authorized by the Constitution or Act of Congress" to provide law enforcement on US soil subject to certain rules. Commented Feb 16, 2018 at 13:22
  • Thanks! I think I framed my question in a poor way. I thought that U.S. military is just prohibited from using force on the territory of U.S. completely (and arrests, or for example warrant execution would requere usage of force). Seems like it is true - but only for civilan law. Commented Feb 17, 2018 at 0:09

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