This appendix provides a broad overview of the Posse Comitatus Act,
which restricts the participation of the military in domestic law
enforcement activities under many circumstances.
The origins of “posse comitatus” are to be found in domestic law.
Black’s Law Dictionary defines the term “posse comitatus” as:
the power or force of the county. The entire population of a county
above the age of fifteen, which a sheriff may summon to his assistance in certain cases as to aid him in keeping the peace, in pursuing and arresting felons, etc.1
The Posse Comitatus Act, 18 U.S. Code, Section 1385, an original
intent of which was to end the use of federal troops to police state
elections in former Confederate states, proscribes the role of the
Army and Air Force in executing civil laws and states:
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 not more than $10,000 or imprisoned not more than two years, or both.2
According to Lujan (1997), the Air Force was added to the original
language in 1956. Although the Navy and Marine Corps are not
included in the act, they were made subject to it by DoD Regulation
(32 C.F.R. Section 213.2, 1992).
KEY EXCEPTIONS TO THE POSSE COMITATUS ACT
A summary of key exceptions to the Posse Comitatus Act follows:3
• National Guard forces operating under the state authority of Title
32 (i.e., under state rather than federal service) are exempt from
Posse Comitatus Act restrictions.
• Pursuant to the presidential power to quell domestic violence,
federal troops are expressly exempt from the prohibitions of
Posse Comitatus Act, and this exemption applies equally to
active-duty military and federalized National Guard troops.4
• Aerial photographic and visual search and surveillance by military personnel were found not to violate the Posse Comitatus
• Congress created a “drug exception” to the Posse Comitatus Act.
Under recent legislation, the Congress authorized the Secretary
of Defense to make available any military equipment and personnel necessary for operation of said equipment for law enforcement purposes. Thus, the Army can provide equipment,
training, and expert military advice to civilian law enforcement
agencies as part of the total effort in the “war on drugs.”
• Use of a member of the Judge Advocate Corps as a special assistant prosecutor, while retaining his dual role in participating in
the investigation, presentation to the grand jury, and prosecution, did not violate Posse Comitatus Act.
• The Coast Guard is exempt from Posse Comitatus Act during
• Although brought under the Act through DoD regulation,
described above, the Navy may assist the Coast Guard in pursuit,
search, and seizure of vessels suspected of involvement in drug
IMPLICATIONS FOR ARMY HOMELAND SECURITY
There is a rather diverse range of potential activities engendered in
each of the homeland security task areas—domestic preparedness,
COG, border and coastal defense, and continuity of operations—that
may involve circumstances in which the Army is asked to assist
domestic law enforcement. Accordingly, it is critical that the Army
develop doctrine, leadership, and training programs that can provide
clear and specific guidance on when and how the Posse Comitatus
Act—as well as any other laws that proscribe Army activities in the
domestic arena—applies and when it does not.