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).

The ability to grant a letter of marque is granted specifically to the U.S. Congress in both the Articles of Confederation and the Constituition, 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.