Brig

In nautical terms, a brig is a vessel with two square-rigged masts. During the Age of Sail, brigs were seen as fast and maneuverable and were used as both naval war ships and merchant ships. They were especially popular in the 18th and early 19th centuries. Brigs fell out of use with the arrival of the steam ship because they required a relatively large crew for their small size and were difficult to sail into the wind. They are not to be confused with a brigantine which has different rigging. The word brig in its most popular present day usage, referring to a military prison on board a United States Navy or Coast Guard vessel, or at an American naval base, derives from the US Navy's use of brigs as prison ships.