Two-masted sailing ship with square rigging on both masts. Brigs were both naval and mercantile vessels. As merchantmen, they often followed coastal trading routes, but ocean voyages were not uncommon, and some were even used for whaling and sealing. Naval brigs carried 10–20 guns on a single deck. In the 18th–19th century, they served as couriers for battle fleets and as training vessels for cadets. Brigs of the early U.S. Navy won distinction on the Great Lakes in the War of 1812. Because square rigging required a large crew, merchant brigs became uneconomical, and in the 19th century they began to give way to vessels such as the schooner and the bark.
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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. While their use stretches back before the 1600s the most famous period of the brig was during the 1800s when they were involved in famous naval battles such as the Battle of Lake Erie. Because they required a relatively large crew and were difficult to sail into the wind (the latter trait is common to all square-rigged ships), brigs were phased out of use by the arrival of the steam boat. They are not to be confused with a brigantine which has different rigging.
Brig sails are named after the masts to which they are attached: the mainsail; above that the main topsail; above that the main topgallant sail; and occasionally a very small sail, called the royal, is above that. Behind the main sail there is a small fore-and-aft sail called the boommainsail (it is similar to the main sail of a schooner). On the foremast is a similar sail, called the trysail. Attached to the respective yards of square-rigged ships are smaller spars, which can be extended, thus lengthening the yard, thus receiving an additional sailing wing on each side. These are called studding sails, and are used with fair and light wind only. The wings are named after the sails to which they are fastened, i.e. the main studding sails, main top studding sails, and the main top gallant studding sails, etc.
The brig’s foremast is smaller than the main mast. The fore mast holds a fore sail, fore top sail, fore top gallant sail, and fore royal. Between the fore mast and the bowsprit are the fore staysail, jib, and flying jib. All the yards are manipulated by a complicated arrangement of cordage named the running rigging. This is opposed to the standing rigging which is fixed, and keeps mast and other things rigid.
The Telos, built in Bangor, Maine in 1883, was reportedly the last brig to join the American merchant marine, and was "considered to be the finest vessel of her class ever constructed in Maine". She was wrecked on Aves Island, off Bonaire in the Caribbean, in 1900.
Note that while the famous ghost ship Mary Celeste is sometimes called a brig, she was probably a brigantine.