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Not Without a Letter of Marque: The Constitutional Requirement Regarding the Use of Armed Private Mi

Disclaimer: The views expressed in this article are those of the author and do not necessarily reflect the views of the USCG, DHS, or the U.S. Federal Government or any Authorized Representative thereof.

By: Daniel Wiltshire


In the last 16 years, the U.S. Military has relied heavily on private military contractors (PMCs) to supplement its all-volunteer force and circumvent caps on deployed military personnel. PMCs have assisted with everything from logistics, to detainee handling and interrogation, to armed protection details.

A recent New York Times editorial by Erik Prince, founder of the PMC Blackwater Worldwide (since renamed to the Academi), advocated for greater reliance on PMCs to facilitate the withdrawal of most U.S. troops from Afghanistan. Mr. Prince advocates that PMCs should not only provide logistical support but should “live, train and patrol alongside” Afghan forces, even fly combat aircraft.

Mr. Prince’s vision of more government-funded PMCs is controversial but not legally untenable. A legal regime exists for using PMCs on land in declared wars and contingency operations. However, what if PMCs sought to take their business-model to sea? In that case, additional constitutional requirements and international norms would apply.

The Demand Will Exist:

The U.S. Navy has fewer ships than needed to meet even peacetime requirements, and recent collisions and engineering casualties illustrate the extent to which it is overtaxed. As the Navy shifts its focus to the Pacific, PMCs will likely seek to expand their operations into that maritime theater. In the event of a major contingency, the Navy may turn to PMCs to supplement its forces just as the Army did in Iraq and Afghanistan.

Current PMC Legal Regime:

Land-based PMCs operate under a domestic legal framework governed by the Federal Acquisition Regulations. PMCs are prohibited from conducting inherently governmental functions, including combat operations. However, OMB Circular A-76 permits “guard services, convoy protection services, plant protection services, pass and identification services, and the operation of . . . detention facilities.” PMCs are also authorized to use deadly force “when necessary to execute their security mission to protect assets/persons. . . .” Due to incidents in Iraq, the UCMJ was amended to apply to PMCs during both war and contingency operations. Notably, the Constitution is silent on hiring private men-at-arms ashore.

Internationally, the Montreux Document (to which the U.S. is a signatory), governs PMC best practices and legal obligations. The Document requires contracting states to hold PMCs to appropriate standards and international humanitarian law and holds states responsible for crimes or breaches of the Geneva Conventions. Mercenaries are prohibited, but “mercenary” is narrowly defined, and PMCs are not mercenaries under Article 47 of Protocol I of the Geneva Conventions if they are citizens of the contracting state.

Legal Regime at Sea:

Additional legal regimes apply to private seaborne men-at-arms. Whereas the Constitution does not address hiring private men-at-arms ashore, it grants Congress authority to issue letters of marque (the means to authorize private men-at-arms at sea). Letters of marque vest in a private entity some of the authority and protections of a state actor in furtherance of military aims.1 Domestically, Article I, Section 8 of the Constitution reserves to Congress the power “[t]o declare War, grant Letters of Marque and Reprisal, and make Rules concerning Captures on Land and Water.”

Prior to the Mid-19th Century, letters of marque were often issued to privateers. Privateers are defined by the Oxford English Dictionary as “[a]n armed vessel owned and officered by private persons, and holding a commission from the government . . . authorizing the owners to use it against a hostile nation, and especially in the capture of enemy merchant shipping.”2 Additionally, vessels holding letters of marque engaged or were engaged by warships, and letters of marque were issued both for the defensive armament of merchant vessels and for the arming of private vessels to engage in anti-piracy.3 Thus, letters of marque provide state-sanctioned armament of private vessels to accomplish government objectives in war, or in activities other than warlike anti-piracy.

In international law, privateering is prohibited by the 1856 Paris Declaration Respecting Maritime Law. Though the U.S. is not a signatory, it has in effect abided by the Declaration and has not commissioned a privateer since the War of 1812.4 However, while the 1856 Paris Declaration prohibits privateering, it neither defines what constitutes a privateer nor explicitly prohibits the issuance of letters of marque. Letters of marque have historically been issued to private vessels for activities other than privateer-like commerce raiding, examples include anti-piracy and self-defense.5 Consequently, although letters of marque have fallen into disuse, they are not explicitly prohibited by international law.

How do PMCs fit into the legal regime?

Armed seaborne PMCs conducting the maritime equivalent of recent armed land-based PMC missions would require a letter of marque to operate legally under U.S. law. Using force at sea in support of state objectives, whether those objectives are defensive or offensive in nature, is the sort of activity traditionally authorized by a letter of marque. Even modern anti-piracy operations would require a letter of marque. However, purely logistical or training activities would not require a letter of marque, as letters of marque were not historically issued to accomplish such tasks.

As a matter of U.S. law, armed seaborne PMCs fall under the same federal contracting regulations as land-based PMCs, but are also subject to the additional Article I, Section 8 requirement to hold a letter of marque. Under international law, a private armed vessel is prohibited if it is a privateer. Consequently, a PMC holding a letter of marque could engage in bellicose activities in compliance with international law as long as it does not conduct activities traditionally carried out by privateers, like attacking merchant shipping. Such a vessel is not prohibited as a mercenary under Article 47 of Protocol I if crewed by citizens of the state that contracted it. Moreover, because the U.S. is not a signatory to the Paris Declaration, vessels holding U.S. letters of marque would not be prohibited from privateering under U.S. law.6

Ultimately, seaborne PMCs are permissible under both domestic and international law, provided that they are issued a letter of marque, contracted in accordance with the FAR and applicable regulations, and overseen as required by the Montreux Document.


Id. at 434-36 (discussing the historical use of letters of marque and/or privateers in combating piracy, as well as the armament of private vessels for defensive purposes and blockade running).

Id. at 427-29 (discussing U.S. use of privateers in the American Revolution, War of 1812, and the U.S. Civil War).

6 See Cooperstein at 231, 251-52 (discussing that the power to issue letters of marque is vested in Congress by the Constitution, such that a Constitutional amendment would be required to remove that power).


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