Features - The Posse Comitatus Act: A Resource Guide

By Stephen Young, Published on February 17, 2003

Stephen Young is a reference librarian at The Catholic University of America, Kathryn J. DuFour Law Library. Stephen has written extensively in the area of United Kingdom law, and has contributed a number of articles to LLRX.com.

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.

                                                                                                The “Posse Comitatus Act” 18 U.S.C. 1385


In the fall of 2002, the Washington DC metro area was subjected to a series of apparently random sniper shootings. During a three week reign of terror the sniper(s) killed 10 victims, seriously wounded four others, and brought a metropolitan area comprising over 4 million people to a standstill. During this period the Secretary of Defense, Donald Rumsfeld, authorized the use of the U.S. Northern Command in supplying “assets and capabilities” to civil law enforcement to help track down the sniper(s). Although military personnel and equipment played no role in the eventual arrest of the two individuals accused of participating in the sniper attacks, John Allen Muhammed and Lee Malvo, the use of Army RC-7 fixed wing aircraft, equipped with high technology sensors and manned by military personnel, provoked charges that the government had violated the Posse Comitatus Act of 1878. The act prohibits the use of the army or the air force to execute the law unless “expressly” authorized by the Constitution or Congress.

This article will briefly discuss the history of the posse comitatus in common law and the development and application of the Posse Comitatus Act of 1878. A select bibliography of law review articles and other secondary sources comprises the majority of the article.

History of the Posse Comitatus in English Law

The term “posse comitatus,” literally translated as the power of the county, first appeared in English law in 1411 with the passage of a riot act calling for the sheriffs and justice of the peace together with the “poair de counte” to arrest rioters (13 Hen. 4, c.7 (1411)). However the concept of a posse comitatus can be traced back to the Assize of Arms (1181) and the creation of the “jurata ad arma,” an armed body of men at the disposal of the King for the purposes of keeping the peace. The role of the jurata ad arma was further cemented with the passage of the Statute of Winchester (13 Edw. 1, stat. 2, c.4 (1285)), a section of which called for the jurata ad arma to respond to the “hue and cry” for the pursuit of malefactors and peacekeeping. However the separation of the military and the militia from civil law enforcement had been developed earlier in the century with the signing of the Magna Carta (1215, revised 1225). Chapter 39 of the revised version of the Magna Carta (1225) prohibited the imprisonment or punishment of a “freeman” except by his peers or the law of the land.

The apparent conflict between the rights enshrined in the Magna Carta and the establishment of a permanent posse comitatus by statutes in the fifteenth and sixteenth centuries continued until the time of the English Revolution in the seventeenth century. By 1623 the statutory basis for the jurata ad arma had been repealed (21 Jac. 1, c.28 (1623)), however King Charles 1 continued to use martial force to control the country. Parliament’s resistance to Charles’ claims to the militia provided one of the major factors leading to the Civil War (1642-48). By the end of the seventeenth century and the restoration of the monarchy the role of the posse comitatus had been more clearly defined, it was to work within the confines of the law and would be separate from a militia. The Bill of Rights (1 W. & Mary, sess.2, c.2 (1688)) further confirmed the exclusion of the military from the role of civil law enforcement.

In the eighteenth century the posse comitatus was once again used to control riots, however the 1714 Riot Act (1Geo. 1, stat.2, c.5 (1714)) clearly intended the posse comitatus to be under the control of civil not military authorities, and for those arrested to be subject to the due process of the law of the land and not martial law. William Blackstone in his Commentaries on the Laws of England, made clear that the separation of the military from civil law enforcement was an essential component of the legal system (1 Comm. 400), however he also recognized the need for a posse comitatus for “keeping the peace and pursuing the felons” (1 Comm. 343).

In 1780 a series of riots in London were eventually suppressed by the use of soldiers. In discussing the legal ramifications of this action Parliament agreed with Lord Chief Justice Mansfield who declared that all civil riots should be put down by civil authorities and the posse comitatus, never by military authorities. Further that even if soldiers comprise the posse comitatus they are deemed to be acting in a civil capacity and are thus subject to civilian laws. This policy of soldier as civilian came to be known as the Mansfield Doctrine and was to be the controlling policy on the role of the posse comitatus in England. For more information on the development of the Mansfield Doctrine see David Engdhal, The Legal Background and Aftermath of the Kent State Tragedy, 22 Cleveland State Law Review 3 (1973). Engdahl also provides a very useful description of the evolution of the posse comitatus in English law in Soldiers Riots and Revolution: The Law and History of Military Troops in Civil Disorders, 57 Iowa Law Review 1 (1971). Another useful history of the topic can be found at the beginning of Charles Doyle’s The Posse Comitatus Act & Related Matters: The Use of the Military to Execute Civilian Law (2000).

The History of the Posse Comitatus in American Law

The American experience with the posse comitatus began in the colonial period with the repeated use of military troops to suppress disorders in the colonies. The violation of the due process principles outlined in colonial charters was most apparent in the Boston massacre of 1770 when rioters were fired upon by the army. The army had been sent to Boston to act as a police force, the responsibility of civil authorities, rather than as a security force. Following the Revolution the founding fathers incorporated strong due process principles into the Constitution, however they also allowed for the use of the militia to execute the laws of the Union (U.S. Const. Art I, s.8, cl.15, 16). David Engdahl provides an excellent summary of the debates over the use of the military and the militia during the Constitutional Convention in Soldiers Riots and Revolution: The Law and History of Military Troops in Civil Disorders, 57 Iowa Law Review 1 (1971).

During the first 70 years of the new country the principles of due process and an adoption of the Mansfield Doctrine prevailed. While militiamen and soldiers were occasionally called to supplement the civilian peace keeping forces they were viewed strictly as a civilian posse and thus held liable under ordinary law. The turning point for this application of the Mansfield Doctrine occurred shortly before the Civil War. A federal marshal, in carrying out provisions of the Fugitive Slave Act 1850, sought reimbursement from the government for funds he had paid a posse comitatus comprised of police and militiamen. In responding to the claim the then U.S. Attorney General, Caleb Cushing, overruled the Mansfield Doctrine and declared that a posse comitatus could consist of soldiers acting in their military capacity (6 Op. Att’y Gen. 466, 473 (1854)). This overhaul of government policy toward a posse comitatus was to continue throughout the Civil War period when the military was used on numerous occasions for apparently civilian peace keeping duty.

The Posse Comitatus Act

The Posse Comitatus Act of 1878 was a direct response to the increasing use of the military for civilian purposes in the Reconstruction period following the Civil War. On many occasions troops had been used to quell civil disturbances, to help form governments in the southern states, and to enforce civil laws. This issue came to a head when Rutherford B Hayes won the disputed presidential election of 1876. Accusations were quickly made that troops sent to the southern states to act as a posse comitatus for federal marshals at the polls assisted in providing the President with the essential votes. In 1878 a Democrat controlled House of Representatives passed an army appropriations bill (20 Stat 145, 152) which contained language expressly prohibiting the use of the army as a posse comitatus. The act therefore rejected the Mansfield Doctrine that troops could be used in a civilian capacity as long as they were subject to civilian law, and equated the use of troops with martial law.

The text of the act has essentially remained unaltered except for the addition of the Air Force in 1956 (70A Stat 626 (1956), however Congress has created expansions to the number of statutory exceptions to the act (e.g., 10 USC 331, 10 USC 332 and 10 USC 371-82).

The Application of the Posse Comitatus Act

The language of the Act calls for two instances when the Act does not apply; when an exception is expressly authorized by the Constitution, and when Congress expressly authorizes an exception. The first of these provisions has created much confusion in the application of the Act since the Constitution contains no provision expressly authorizing the use of the military to enforce the law. Much of the literature discussing the constitutional exceptions of the Act therefore focuses upon the conflict between the implied and inherent constitutional powers of the President as Commander-in-Chief of the armed forces.

The second provision allowing for exceptions to the Act, Congressional authorization, has been applied in two ways; by providing a branch of the armed services with civilian law enforcement capabilities, and by establishing rules for specific types of assistance, thereby tailoring specific statutory exceptions to fit particular circumstances. In the first instance Congress has expressly authorized the Coast Guard to carry out law enforcement duties during peacetime, most notably enforcement of anti-drug laws (14 USC 2). In times of war authority for the Coast Guard transfers from the Department of Transportation to the Navy, however under the statutory exceptions created by Congress the Coast Guard can still fulfill its law enforcement duties. It should be noted that the Navy and Marine Corps have been brought under the Posse Comitatus Act by DoD Directive 5525.5 (1986, as amended 1989) and by Secretary of the Navy Instruction (SECNAVINST) 5820.7B (1988).

Second, Congress has enacted numerous pieces of legislation permitting the use of military assistance and equipment in aiding civilian law enforcement (see in particular 10 USC 371-82). Most of this legislation originated in 1981 following the “Wounded Knee” cases. These cases stemmed from the 1973 take-over of a facility on the Pine Ridge Reservation in South Dakota, and the subsequent siege, arrest and trial of members of the American Indian Movement (AIM). During the course of the siege the federal civilian law enforcement authorities made extensive use of material, personnel and equipment provided by the military. The assistance provided by the military ultimately led to the undermining of the charges against those arrested, and it became clear that Congress needed to address the need for statutory exclusions to the original Act. In addition to statutory exceptions concerning providing civil law enforcement with assistance, Congress has also enacted legislation providing for exceptions during times of civil disturbance (10 USC 331, 10 USC 332). The regulations promulgated under these statutes provide for the protection of federal property and government functions, and authorizes the use of the military in states of emergency when civil authorities are unable to control the situation (32 CFR 215.1-.10). Additional legislation has been enacted covering instances when nuclear material is involved in an emergency (18 USC 831(e)).


At first glance it would appear that the Posse Comitatus Act 1878 embodies the principle of the separation of the military from civilian law enforcement, a principle that has been an essential component of Anglo-American legal history since the Magna Carta. However, it is interesting to note that no one has ever been convicted of violating 18 USC 1385, and when needed Congress has been quick to create statutory exceptions as permitted by the Act. The Act has therefore succeeded in putting forth an ideal, but has fallen woefully short in creating a practical, legal impediment to the use of the military for civil law enforcement. It could even be argued that the Act has only served to legitimize the military role of a posse comitatus by providing Congress with the ability to create its own exceptions whenever the need arises. It will be interesting to see whether the Act continues to receive heightened attention over the next few years, and whether demands for amendments to and/or repeal of the Act are raised.

Primary Documents Relating to The Posse Comitatus Act 1878

Original Statute

June 18, 1878, ch. 263 §15, 20 Stat. 152 (Army Appropriations)

March 3, 1899, ch. 429, § 362, 30 Stat. 1325 (Suppression of Riots)

June 6, 1900, ch. 768, § 29, 31 Stat. 330 (Alaska Provision)

Removed from Title 10 and added to Title 18: August 10, 1956, ch. 1041, § 18(a), 70A Stat. 626


June 25, 1959, P.L. 86-70, §17(d), 73 Stat. 144: Removed the reference to Alaska

September 13, 1994, P.L. 103-322, Title XXXIII, § 330016(1)(L), 108 Stat. 2147: Replaced “not more than $10,000” with “under this title.”

Statutory Exceptions

Military Support for Civilian Law Enforcement Agencies, 10 USC 371-82.
December 1, 1981, P.L. 97-86, Title IX, § 905(a)(1), 95 Stat. 1114.
Substantive amendments include: Defense Drug Interdiction Assistance Act October 27, 1986, P.L. 99-570, Title III, Subtitle A, § 3053(b)(2), 100 Stat. 3207-76; Department of Defense Authorization Act September 29, 1988 P.L. 100-456, Div A, Title XI, § 1104(a), 102 Stat. 2043.

Insurrection, 10 USC 331-2.
August 10, 1956, ch.1041, § 1, 70A Stat. 15.
Substantive Amendments include: Defense Officer Personnel Management Act: December 12, 1980, P.L. 96-513, Title V, Part B, §511(11)(c), 94 Stat. 2921.

Select Congressional Documents

Investigation of Employment of Armed Bodies of Men. Senate Document 57. 1893.

The Posse Comitatus Act. Hearings Before the House Committee on the Judiciary, Subcommittee on Crime. June 3, 1981.

Department of Defense Authorization Act 1982. Report of the House Committee on the Judiciary, H.Rpt. 97-71 pt.2. June 12, 1981.

Military Cooperation with Civilian Law Enforcement. Hearings Before the House Committee on the Judiciary, Subcommittee on Crime. July 28, 1983.

Military Cooperation with Civilian Law Enforcement. Hearings Before the House Committee on the Judiciary, Subcommittee on Crime. April 24, 1985.

The Role of the Military in Drug Interdiction. Hearings Before the Defense Policy Panel, and the Subcommittee on Investigations, House Armed Services Committee. May 10, June 9, 1988.

The Role of the Military in Drug Abuse Prevention. Hearings Before the Senate Armed Services Committee. June 14, 1988.

Role of the Department of Defense in Drug Interdiction. Hearings before the Senate Armed Services Committee, and the Subcommittee on Investigations, House Armed Services Committee. June 15, 1988.

Narcotics Interdiction and the Use of the Military: Issues for Congress. Committee print issued by the House Committee on Armed Services. August 24, 1988.

Related Regulations

Employment of Military Resources in the Event of Civil Disturbances, 32 CFR 215.

Employment of Troops in Aid of Civil Authorities, 32 CFR 501.

DoD Cooperation With Civilian Law Enforcement Officials, 32 CFR 213, removed by 53 Fed. Reg. 23776 (April 28, 1993)

Documents from The Department of Defense and The Armed Forces

Civil Disturbances, Army Regulation 500-50 (1972).

Support to Civilian Law Enforcement, Army Regulation 500-51 (1983).

Civil Disturbances, Department of the Army Field Manual (FM) 19-15 (1985)

Cooperation With Civilian Law Enforcement Officials, Secretary of the Navy Instruction 5820.7B (1988).

DoD Cooperation With Civilian Law Enforcement Officials, DoD Directive Number 5525.5 (1986, amended 1989). This directive essentially replaced 32 CFR 213.

Military Support to Civil Authorities (MSCA), DoD Directive Number 3025.1 (1993).

Military Assistance for Civil Disturbances (MACDIS), DoD Directive Number 3025.12 (1994).

Military Assistance to Civil Authorities, DoD Directive Number 3025.15 (1997).

Attorney General Opinions

Extradition of Fugitives from Service, 6 Op. Att’y Gen. 466 (1854).

Insurrection in a State, 8 Op. Att’y Gen. 445 (1854).

Employment of the Military as a Posse, 16 Op. Att’y Gen. 162 (1878).

Suppression of Lawlessness in Arizona, 17 Op. Att’y Gen. 333 (1882).

Marshal of Indian Territory, 19 Op. Att’y Gen. 293 (1889).

Employment of United States Troops in Alaska, 19 Op. Att’y Gen. 368 (1889).

Indian Territory – Use of Military, 21 Op. Att’y Gen. 72 (1894).

President’s Power to Use Federal Troops to Suppress Resistance to Enforcement of Federal Court Orders – Little Rock, Arkansas, 41 Op. Att’y Gen. 313 (1957)

Landmark Judicial Decisions

The following represent only select, landmark cases interpreting the Posse Comitatus Act 1878 and should therefore not be viewed as a comprehensive guide to caselaw on the topic.

Laird v. Tatum (1972 US Sct) 408 US 1.

The Wounded Knee Cases

United States v. Yunis (1991 US App, DC) 924 F2d 1086.

United States v. Walden (1974 CA 4, VA) 490 F2d 372.

United States v. Walden (1974 CA 4, VA) 490 F2d 372.

A Select Bibliography of Secondary Resources