Letters of Marque – more properly called "Letters of Marque and Reprisal" originated in 1243 when King Henry III of England issued licenses to specific individuals to seize enemy cargoes at sea and split the proceeds from the sale of those cargoes with the Crown. Later, in 1354, King Edward III broadened the scope of these licenses to authorize a subject to make reprisals against the citizens and possessions of a hostile nation for alleged injuries perpetrated against the king by that nation. While at the time the reprisal could take place on land or sea, early on the term came to apply only to measures taken at sea. Those in possession of a highly coveted letter of marque became known as privateers, and the practice was quickly adopted by most European maritime nations and became a mainstay of international law.
Perhaps unwittingly – although probably not – the Plantagenet king had opened wide a treasure trove of opportunity and profit for the private sector and for the Royal Exchequer. Throughout the Middle Ages enterprising English sea captains operated with the tacit understanding of their king if not his outright commission in harassing the maritime trade of offending nation-states. Things reached a fever pitch when privateers such as Sir Francis Drake seized Spanish ships laden with gold and silver on their return voyage from South America and the Spanish Main. Queen Elizabeth I was only too happy to accept this Midas touch and share in the bounty of the captured treasure and subsequent sale of the seized vessel, its value determined by newly developed Admiralty Courts (also known as "prize courts"). The privateer's captain and crew all received a share based on rank, so everyone was happy – except, of course, the captain and crew of the captured vessel and the Court of King Phillip II of Spain. His displeasure led ultimately to the defeat of the Spanish Armada, one of most colossal and humiliating defeats in military history.
A letter of marque thus conferred on the private merchant vessel a quasi-naval status, to the point where it was equipped with naval-style guns, often the 6- or 12-pounder variety. (A 6-pounder gun, for example, fired a shot that weighed six pounds.) A commissioned privateer was afforded the full protection of the rules of war, and captured privateers were treated (in theory at least) as prisoners of war. Unlike a naval vessel, however, the primary objective of a privateer was not to engage and destroy the enemy. A privateer's prime objective was to board an enemy merchantman having caused as little damage as possible to its top-hamper and hull (so to not damage the selling price) and claim it as a prize of war. If an enemy naval vessel looked on the horizon, a privateer would normally clap on all sail and run, no matter how heavily armed it might be.
During the American Revolution, letters of marque were issued by state legislatures and by the Continental Congress. Such was the lure of quick and substantial profits, privateering made it increasingly difficult for the Continental navy to recruit sailors. The navy also seized British merchantmen, but not as a prime objective and not with as generous a split of earnings among the ship's company.
The French term for a letter of marque is "lettre de course", a term which gave rise to the word "corsair" as a synonym to "privateer."
Originally published williamchammond.blogspot.co.uk