Letter of marque

A letter of marque is an authorization given to a private ship owner and/or ship's captain by a government. The authorization allows the ship to act as a ship of war in naval engagements with the ships of another nation. A letter of marque would allow, for example, a private ship to engage a cargo ship and sink it, seize its cargo, or take its crew prisoner (or any combination of these).

International status

The Declaration of Paris (1856) effectively abolished privateering amongst its signatories. The United States was not a signatory and thus technically remains able to issue letters of marque.

A rationale for the letter, especially in the context of reprisal, takes place when "a nation concludes that another has injured it, granting letters of marque and reprisal to select individuals can be a measured means of seeking recompense—more harsh than negotiations but less extreme than a full-scale war."

Modern maritime conditions and naval tactics may make the concept less practical. A privateer might be authorized, but its movement, on radar or other sensors used by military ships, might appear be that of a pirate. The privateer might be intercepted, wasting time, or even taken under fire.

Further, just as there is question of the status of both defined mercenaries and of private military contractors under the Third Geneva Convention, it is not at all clear that an independently operating privateer would meet the requirements of being a lawful combatant.

United States

The ability to grant letters of marque and reprisal is granted specifically to the U.S. Congress in both the Articles of Confederation and the Constitution, and also specifically denied to the states in both documents. The ability to grant a letter of marque is noted as one of the War Powers. While the two are similar, the concept of reprisal developed earlier, as an authorization for private ships to arm themselves for self defense. A letter of marque authorizes the vessel to take offensive action against ships either of pirates or national enemies, the latter when a full state of war might not exists.

U.S Congressman Ron Paul (Republican of Texas) has proposed using letters of marque to fight terrorism and piracy, most recently in response in response to the attack on the MV Maersk Alabama in April of 2009.