Letter-of-marque

In the days of fighting sail, a letter of marque and reprisal was a government license authorizing a person (known as a privateer) to attack and capture enemy vessels and bring them before admiralty courts for condemnation and sale. Cruising for prizes with a letter of marque was considered an honorable calling combining patriotism and profit, in contrast to unlicensed piracy, which was universally reviled. In addition to the term lettre de marque, the French sometimes used the term lettre de course for their letters of marque. "Letter of marque" was sometimes used to describe the vessel used: a "letter of marque" generally refers to a lumbering square-rigged cargo carrier that might pick up a prize if the opportunity arose. A "privateer" was a fast and weatherly fore-and-aft-rigged vessel heavily armed and heavily crewed, intended exclusively for fighting.

A "letter of marque and reprisal" would include permission to cross an international border to effect a reprisal (take some action against an attack or injury) authorized by an issuing jurisdiction to conduct reprisal operations outside its borders.

Old English mearc, from Germanic *mark- ‘boundary; boundary marker’, from Proto-Indo-European *merǵ- ‘boundary, border’.

French, from Provençal marca, from marcar ‘seize as a pledge‘

According to the Oxford English Dictionary, the first recorded use of "letters of marque and reprisal" was in an English statute in 1354 during the reign of Edward III. The phrase referred to "a licen[c]e granted by a sovereign to a subject, authorizing him to make reprisals on the subjects of a hostile state for injuries alleged to have been done to him by the enemy's army."

During the Middle Ages, armed private vessels enjoying their sovereign's tacit consent, if not always an explicit formal commission, regularly raided shipping of other nations, as in the case of Francis Drake's attacks on Spanish shipping, of which Elizabeth I (despite protestations of innocence) took a share.Grotius's 1604 seminal work on international law, De Iure Praedae (Of The Law of Prize and Booty), was an advocate's brief defending Dutch raids on Spanish and Portuguese shipping.

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Wikipedia