Privateer
A privateer (sometimes called corsair or buccaneer) was a private person or ship authorized by a government by letters of marque to attack foreign vessels during wartime, and take them as prizes. Captured ships were subject to condemnation and sale under prize law, with the proceeds divided between the privateer shipowners and crew. Privateering was a way of mobilizing armed ships and sailors as naval auxiliaries.
Historically, the distinction between a privateer and a pirate has been blurred, sometimes depending on the source as to which label was correct. At times, pirates sought dubious government sanction to operate under a veil of legitimacy.
Legal framework
The letter of marque of a privateer would typically limit activity to the ships of specific nations. Typically, the owners or captain would be required to post a performance bond, or they might be liable to pay damages to an injured party. In the United Kingdom, letters of marque were revoked for various offences.
Some crews were treated as harshly as naval crews of the time, while others followed the comparatively relaxed rules of merchant ships. Some crews were made up of professional merchant seamen, others of pirates, debtors, and convicts. Some privateers ended up becoming pirates, not just in the eyes of their enemies but also of their own nations. William Kidd, for instance, began as a legitimate British privateer but was later hanged for piracy.