Privateers the legal pirates

A privateer or "corsair" was a private person or ship authorized by a government by letters of marque to attack foreign vessels during wartime.

Privateering was a way of mobilizing armed ships and sailors without having to spend treasury resources or commit naval officers. They were of great benefit to a smaller naval power or one facing an enemy dependent on trade: they disrupted commerce and pressured the enemy to deploy warships to protect merchant trade against commerce raiders.

An action between an English ship and Privateers

 The cost was borne by investors hoping to profit from prize money earned from captured cargo and vessels. The proceeds would be distributed among the privateer's investors, officers, and crew.

Privateers were part of naval warfare from the 16th to the 19th centuries. Some privateers have been particularly influential in the annals of history. Sometimes the vessels would be commissioned into regular service as warships. The crew of a privateer might be treated as prisoners of war by the enemy country if captured.

French Privateers in 1806 taking prizes and British prisoners

Historically, the distinction between a privateer and a pirate has been, practically speaking, vague, often depending on the source as to which label was correct in a particular circumstance. 

Privateers search Spanish ladies for their jewels in Ecuador, 1709

The actual work of a pirate and a privateer is generally the same (raiding and plundering ships); it is, therefore, the authorization and perceived legality of the actions that form the distinction. At various times, governments indiscriminately granted authorization for privateering to a variety of ships, so much so that would-be pirates could easily operate under a veil of legitimacy.

 A privateer vessel commanded by French corsair, 1800