What is a Privateer? When do they become pirates?

Hitting its peak in the 16th and 17th centuries privateering became a huge asset to many countries looking to supplement their naval forces. Captains/officers of ships they personally owned, were hired (commissioned) by various governments around the world to prey upon enemy vessels. They were granted an official document known as a Letter of Marquee. Said document outlined that a specific ship and it's crew could lay siege to vessels threatening the commissioning country's interests, and granted immunity from being tried for piracy. Additionally, the Letter of Marquee would specify which government's vessels could be legally captured. They did so to interrupt trade routes used by rival countries, and gain renown for their naval strength; which no doubt helped in the general defense of their own country, as well as disrupted the economies of their competition.

As prize ships were taken, they were brought in to the ports of the capturing privateer's government. After examining the capturing captain's Letter of Marquee to make sure it wasn't a forgery, the prize ship itself would then be evaluated and it's crew questioned; to see if it was a vessel belonging to a country named on the Letter of Marquee. This process could take a while, however, once it was proven to be in order the cargo would be sold and the vessel was free to be claimed. Sometimes the owner of the vessel would reclaim it.

The Captain/officer of the capturing privateer ship was granted the money from the captured vessel. After paying dues to the hiring government, the privateer would divide the rest of the spoils amongst the crew. This helped the country gain more military funds and provided a lucrative vocation to the privateer and his crew. However during peacetime some privateers lost their Letter of Marquee. Many of these former privateers turned to piracy as a result. Their actions were often times overlooked, as long as the newly formed pirates remained loyal to their country's crown. It was a risk, the Letter of Marquee protected privateers from execution, following the Rules of War, if a country did capture a vessel and it was found that they had a valid letter, the captured crew were treated as prisoners of war. If they did not have a valid document they were considered pirates and executed immediately. Privateering and its regarding laws were followed by many countries until the early 19th century.

Fun Fact:

Privateers played a major part in both the Revolutionary War and the Civil War. Confederate President Jefferson Davis commissioned privateers to attack Union ships. Preventing much needed supplies from reaching their destination.