Posse Comitatus Act

Limits on federal use of the military for law enforcement

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The Posse Comitatus Act is a United States federal law (18 U.S.C. § 1385) passed on June 16, 1878 after the end of Reconstruction. The Act was intended to prohibit Federal troops from supervising elections in former Confederate states. It generally prohibits Federal military personnel and units of the United States National Guard under Federal authority from acting in a law enforcement capacity within the United States, except where expressly authorized by the Constitution or Congress. The Posse Comitatus Act and the Insurrection Act substantially limit the powers of the Federal government to use the military for law enforcement.

The original act referred only to the United States Army. The Air Force was added in 1956, and the Navy and the Marine Corps have been included by a regulation of the Department of Defense. The United States Coast Guard is not included in the act as it has federal law enforcement duties as part of its primary mission. This law is often mentioned when it appears that the Department of Defense is interfering in domestic disturbances.

In 1971, Deputy Secretary of Defense David Packard wrote the Packard Memo or Employment of Military Resources in the Event of Civil Disturbances which modified the Code of Federal Regulations, Title 32, Volume 2, Chapter 1, Part 215, Section 6. This addition revoked a substantial part of the 1878 Posse Comitatus Act providing for 'exceptions' to the Act "to prevent loss of life or wanton destruction of property and to restore governmental functioning and public order when sudden and unexpected civil disturbances, disasters, or calamities seriously endanger life and property and disrupt normal governmental functions to such an extent that duly constituted local authorities are unable to control the situation" and "to protect Federal government functions when the need for protection exists". "Packard's directive (stated) that turning over law enforcement will 'normally' require a Presidential Executive Order, but that this requirement can be waived in 'cases of sudden and unexpected emergencies... which require that immediate military action be taken." (Lindorff, 1988) Packard's directive, in essence, reinstated the possibility of martial law in the United States, prohibited since 1878. "Martial law was defined in an integral Federal Emergency Management Agency (FEMA) memo written in 1982... The memo, written by FEMA official John Brinkerhoff to agency director Louis Giuffrida, notes that martial law “suspends all prior existing laws, functions, systems, and programs of civil government, replacing them... with a military system.” (Lindorff, 1988).

The Law

The text of the relevant legislation is as follows:

Sec. 1385. - Use of Army and Air Force as posse comitatus

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.

Also notable is the following provision within Title 10 of the United States Code (which generally concerns organization and regulation of the armed forces and Department of Defense):
[10 U.S.C.] § 375. Restriction on direct participation by military personnel

The Secretary of Defense shall prescribe such regulations as may be necessary to ensure that any activity (including the provision of any equipment or facility or the assignment or detail of any personnel) under this chapter does not include or permit direct participation by a member of the Army, Navy, Air Force, or Marine Corps in a search, seizure, arrest, or other similar activity unless participation in such activity by such member is otherwise authorized by law.

Limits on the Act

There are a number of situations in which the Act does not apply. These include:

  • National Guard units while under the authority of the governor of a state
  • Troops when used pursuant to the Federal authority to quell domestic violence as was the case during the 1992 Los Angeles riots;
  • Troops used under the order of the President of the United States pursuant to the Insurrection Act
  • Under 18 U.S.C. § 831, the Attorney General may request that the Secretary of Defense provide emergency assistance if civilian law enforcement is inadequate to address certain types of threat involving the release of nuclear materials, such as potential use of a Nuclear or Radiological weapon. Such assistance may be by any personnel under the authority of the Department of Defense, provided such assistance does not adversely affect U.S. military preparedness.
The John Warner National Defense Authorization Act for Fiscal Year 2007 (H.R. 5122), which was signed into law on Oct 17, 2006, allowed the U.S. military to seize control immediately after a natural disaster. This change was rully repealed by HR 4986: National Defense Authorization Act for Fiscal Year 2008.

Exclusion Applicable to U.S. Coast Guard

Although it is a military force, the United States Coast Guard, which operates normally under the Department of Homeland Security, is not covered by the Posse Comitatus Act and does enforce U.S. laws. It enforces U.S. laws even when operating as a service in the Navy.

In December 1981 additional laws were enacted clarifying permissible military assistance to civilian law enforcement agencies and the Coast Guard especially in combating drug smuggling into the United States. Posse Comitatus clarifications emphasize supportive and technical assistance (e.g., use of facilities, vessels, aircraft, intelligence, tech aid, surveillance) while generally prohibiting direct participation of Department of Defense personnel in law enforcement (e.g., search, seizure, and arrests). For example, a US Navy vessel may be used to track, follow and stop a vessel suspected of drug smuggling, but a Coast Guard Law Enforcement Detachments (LEDETS) aboard the Navy vessel would perform the actual boarding and, if needed, arrest the crew.


  • Section 1385 of title 18 (commonly known as the Posse Comitatus Act) prohibits the use of the Armed Forces as a Posse comitatus to execute the laws except in cases and under circumstances expressly authorized by the Constitution or Act of Congress.
  • Enacted in 1878, the Posse Comitatus Act was expressly intended to prevent United States Marshals, on their own initiative, from calling on the Army for assistance in enforcing Federal law.
  • Some believe the Posse Comitatus Act has served the Nation well in limiting the use of the Armed Forces to enforce the law. Whether this is a good thing or not is subject to debate.
  • The Posse Comitatus Act was not intended to be a complete barrier to the use of the Armed Forces for a range of domestic purposes, including law enforcement functions, when the use of the Armed Forces is authorized by Act of Congress or the President determines that the use of the Armed Forces is required to fulfill the President's obligations under the Constitution provide for the common defense or to respond promptly to insurrection, or other serious emergency.
  • Existing laws, including Title 10, Chapter 15 (commonly known as The Insurrection Act), and The Robert T. Stafford Disaster Relief and Emergency Assistance Act (Title 42, Chapter 68), grant the President broad powers that may be invoked in the event of domestic emergencies, including an attack against the Nation using weapons of mass destruction, and these laws specifically authorize the President to use the Armed Forces to help restore public order.
  • The Posse Comitatus Act could be replaced, nullified or modified by a simple act of Congress.
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