The term brig has two definitions based in nautical language. In the first meaning, brig refers to a double masted sailing ship with square-rigged masts. The second definition of the term refers to a military prison under the jurisdiction of the U.S. Navy (USN), the U.S. Coast Guard (USCG), or the U.S. Marine Corps (USMC). The two definitions are tied together in that the use of the word brig to describe a military prison dates back to the use of a brig sailing ship as a prison ship.
This sailing vessel is easily distinguished from other ships by the presence of two masts and a unique rigging. Other comparably sized sailing ships typically have a three-mast system. The brigantine sailing vessel is a related ship, but the rigging of the brigantine differs from the dual square-masted rigging of brigs. The brig uses several smaller sails, while the brigantine uses a square mast on the fore mast and fore-and-aft triangular shaped rigging on the main mast.
The dual square-mast rigging of these sailing vessels gives them certain advantages over the brigantine ships. The use of numerous sails provides faster reaction times to facilitate better handling. Due to the smaller size of the sails, the brig's rigging can be handled by a much smaller crew than that of the brigantine. The typical ship can effectively operate with a crew of 12 to 16 members. Even with the smaller crew size in comparison to other ships, however, the brig's crew is considered large for the size of the ship.
A uniquely designed ship, this vessel is designed for both sailing and rowing. This design made the ship quite useful for military prison operations because prisoners could be forced to work at rowing the vessel. It also made these ships a useful part of the cargo shipping industry because traders could maneuver the ships into places that traditional sailing ships could not effectively reach.
In military usage, these ships were sometimes outfitted as warships. Brigs sometimes carried between 10 and 18 guns, making them a deadly adversary against larger sailing rigs that could not outmaneuver the smaller craft. Due to the ship's precise handling and speed, the brig fell into favor with pirates outside of the Americas and the Caribbean. These ships continued to see use in military and cargo operations until the mid 1800s, when gaff sail ships and steam powered boats began to replace the craft.