Article 1, Section 8, line 11 of the US Constitution states that Congress shall have the power:
“To declare War, grant Letters of Marque and Reprisal, and make Rules concerning Captures on Land and Water.”
“Letters of Marque and Reprisal” are the official way a pirate becomes a privateer, authorized to capture foreign vessels. The most famous privateer, of course, was, Sir Francis Drake:
Sir Francis Drake, vice admiral (c. 1540 – 28 January 1596) was an English sea captain, privateer, navigator, slaver, and politician of the Elizabethan era. Drake carried out the second circumnavigation of the world in a single expedition, from 1577 to 1580, and was the first to complete the voyage as captain while leading the expedition throughout the entire circumnavigation. With his incursion into the Pacific Ocean, he inaugurated an era of privateering and piracy in the western coast of the Americas—an area that had previously been free of piracy.
Specifically, he inaugurated the Age of Piracy in the Pacific by introducing non-Spanish ships into the ecosystem.
In 1243, King Henry III authorized the first privateers in English law, and the crown began issuing official Letters of Marque in 1295. These early letters authorized a kind of “private war,” allowing their recipients to avenge themselves against some foreign ship or ships of a foreign nation more generally for some previous harm. (Until 1620, an application for Letters of Marque had to include the shipowner’s estimate of losses they had previously suffered at the target’s hands.)
By the 16th century, the Letters had shifted from serving purely personal interests to allowing private shipowners to become a kind of auxillary navy, capturing the ships of enemy nations and profiting from the sale of their goods.
Business could be quite profitable for these “legal pirates”–for example, the tiny, Channel Island of Guernsey netted 900,000 Pounds worth of American and French ships during the American Revolution.
Like modern day mercenaries, enterprising pirates like Jean Lafitte who wished to practice their profession with less risk of being hanged by land-based authorities, shopped around from country to country for Letters of Marque. When one war ended and hostilities ended between two countries, privateers moved on to the next conflict, and offered their services to the new countries involved. After his employ by the Americans during the War of 1812, Lafitte offered his services to the Spanish against Mexican revolutionaries, giving himself cover to establish a smuggling station in Galveston, Texas (then part of Spain.) When he was driven from Galveston, he offered his services to the Cubans, and when they tired of him, he obtained Letters from Colombia.
At times, the Letters of Marque seem to have been used less against legitimate enemies of the state and more for pure gain:
The East India Company arranged for letters of marque for its East Indiamen such as the Lord Nelson, not so that they could carry cannons to fend off warships, privateers, and pirates on their voyages to India and China—that they could do without permission—but so that, should they have the opportunity to take a prize, they could do so without being guilty of piracy.
That said, Letters of Marque did obligate their holders to observe the rules of war toward the sailors (and vessels) they captured, rather than massacre them in the piratical way. Captured sailors and other passengers were supposed to be treated as prisoners of war and returned unharmed to land. Admiralty Courts could revoke the letters–and even fine privateers–if they did not. Similarly, privateers could not just abscond with captured goods, but had to turn them over to the Admiralty Courts, which would auction them off and then give the privateers part of the profits.
Likewise, if the navy of a foreign country captured a ship bearing Letters of Marque, they were supposed to not just execute the sailors but treat them like POWs. However, in many cases countries did not recognize the validity of other countries’ Letters, partly because they didn’t recognize those countries and partly because they were at war with them. During the Civil War, the Union charged a crew of Confederate privateers with piracy and threatened to hang them. The case was only resolved in the privateers’ favor when Confederate president Jefferson Davis threatened to retaliate by hanging Union POWs.
The infamous Captain William Kidd, though he had an official Letter of Marque signed by King William III of England, was hanged as a pirate in 1701. Whether Kidd was actually a pirate or just a privateer who was unjustly accused is still a matter of debate.
Letters of Marque fell out of fashion after the end of the Crimean War in 1856, (though land-locked and navy-free Bolivia was still issuing them in 1879 to anyone willing to attack Chilean ships.) The US government hasn’t issued any Letters since 1815, but there was some confusion during WWII about whether the Goodyear Blimps were official privateers.
This was not as absurd as it sounds–the confusion arose because the blimps, with armed civilian crews, were flying anti-submarine patrols off the coast of California. But they had not been issued official Letters of Marque, and so were not privateers.
Ron Paul, a Constitutionally-interested guy, has tried to revive Letters of Marque to fight against “air pirates” like the 9-11 attackers. Similar to hiring Blackwater in Iraq, his proposal would have let the president issue Letters of Marque against specific terrorists and Somali pirates. But so far, his bills have not become laws and Letters of Marque have not returned.