A boom or a chain (also boom defence, harbour chain, river chain, chain boom, boom chain or variants) is an obstacle strung across a navigable stretch of water to control or block navigation. They are sometimes mixed with pile barrages. In modern times they usually have civil uses, such as to prevent access to a dangerous river channel. But, especially historically, they have been used militarily, with the goal of denying access to an enemy's ships: a modern example is the anti-submarine net. Booms have also been used to force passing vessels to pay a toll.

Description

A boom generally floats on the surface, while a chain can be on the surface or below the water. A chain could be made to float with rafts, logs, ships or other wood, making the chain a boom as well.

Historical uses

Especially in medieval times, the end of a chain could be attached to a chain tower or boom tower. This allowed safe raising or lowering of the chain, as they were often heavily fortified. By raising or lowering a chain or boom, access could be selectively granted rather than simply rendering the stretch of water completely inaccessible. The raising and lowering could be accomplished by a

windlass The windlass is an apparatus for moving heavy weights. Typically, a windlass consists of a horizontal cylinder (barrel), which is rotated by the turn of a crank or belt. A winch is affixed to one or both ends, and a cable or rope is wound arou ...

mechanism or a capstan. Booms or chains could be broken by a sufficiently large or heavy ship, and this occurred on many occasions, including the siege of Damietta, the

raid on the Medway The Raid on the Medway, during the Second Anglo-Dutch War in June 1667, was a successful attack conducted by the Dutch navy on English warships laid up in the fleet anchorages off Chatham Dockyard and Gillingham in the county of Kent. At th ...

and the Battle of Vigo Bay. Frequently, however, attackers instead seized the defences and cut the chain or boom by more conventional methods. The boom at the

siege of Derry The siege of Derry in 1689 was the first major event in the Williamite War in Ireland. The siege was preceded by an attempt against the town by Jacobite forces on 7 December 1688 that was foiled when 13 apprentices shut the gates. Thi ...

, for example, was cut by sailors in a

longboat A longboat is a type of ship's boat that was in use from ''circa'' 1500 or before. Though the Royal Navy replaced longboats with launches from 1780, examples can be found in merchant ships after that date. The longboat was usually the largest bo ...

. As a key portion of defences, booms were usually heavily defended. This involved shore-based chain towers,

artillery Artillery consists of ranged weapons that launch Ammunition, munitions far beyond the range and power of infantry firearms. Early artillery development focused on the ability to breach defensive walls and fortifications during sieges, and l ...

batteries, or forts. In the

Age of Sail The Age of Sail is a period in European history that lasted at the latest from the mid-16th (or mid-15th) to the mid-19th centuries, in which the dominance of sailing ships in global trade and warfare culminated, particularly marked by the int ...

, a boom protecting a harbour could have several ships defending it with their broadsides, discouraging assaults on the boom. On some occasions, multiple booms spanned a single stretch of water.

Gallery

File:Capturing Damiate.jpg, Crusaders break a chain protecting the harbour (at left) in the siege of Damietta. File:Boom Towers, Norwich - geograph.org.uk - 177643.jpg, Boom towers in

Norwich Norwich () is a cathedral city and district of the county of Norfolk, England, of which it is the county town. It lies by the River Wensum, about north-east of London, north of Ipswich and east of Peterborough. The population of the Norwich ...

File:Chain Bosphorus.JPG, Remains of the great chain that protected the

Golden Horn The Golden Horn ( or ) is a major urban waterway and the primary inlet of the Bosphorus in Istanbul, Turkey. As a natural estuary that connects with the Bosphorus Strait at the point where the strait meets the Sea of Marmara, the waters of the ...

File:The Great Chain Today.jpg, A preserved section of the

Hudson River Chain The Hudson River Chains were a series of boom (navigational barrier), chain booms constructed across the Hudson River at West Point, New York, West Point by Continental Army forces from 1776 to 1778 during the American Revolutionary War. These s ...

File:Shoebury Boom - geograph.org.uk - 915365.jpg, Remains of the Shoeburyness Boom, built to protect the

Thames Estuary The Thames Estuary is where the River Thames meets the waters of the North Sea, in the south-east of Great Britain. Limits An estuary can be defined according to different criteria (e.g. tidal, geographical, navigational or in terms of salinit ...

from Soviet submarines during the

Cold War The Cold War was a period of global Geopolitics, geopolitical rivalry between the United States (US) and the Soviet Union (USSR) and their respective allies, the capitalist Western Bloc and communist Eastern Bloc, which lasted from 1947 unt ...

Examples

Historical

*The entrance to the Cothon at Carthage was protected by a chain. *The chain at Fort Blockhouse, protecting

Portsmouth Harbour Portsmouth Harbour is a / biological Site of Special Scientific Interest between Portsmouth and Gosport in Hampshire. It is a Ramsar site and a Special Protection Area. It is a large natural harbour in Hampshire, England. Geographically it ...

from 1431 to 1539. *The Leonine Wall included a chain blocking the

Tiber The Tiber ( ; ; ) is the List of rivers of Italy, third-longest river in Italy and the longest in Central Italy, rising in the Apennine Mountains in Emilia-Romagna and flowing through Tuscany, Umbria, and Lazio, where it is joined by the R ...

*A chain spanned the

*A chain and boom blocked the

River Medway The River Medway is a river in South East England. It rises in the High Weald AONB, High Weald, West Sussex and flows through Tonbridge, Maidstone and the Medway conurbation in Kent, before emptying into the Thames Estuary near Sheerness, a to ...

during the

Raid on the Medway The Raid on the Medway, during the Second Anglo-Dutch War in June 1667, was a successful attack conducted by the Dutch navy on English warships laid up in the fleet anchorages off Chatham Dockyard and Gillingham in the county of Kent. At th ...

*The chain blocking the Parana River during the Battle of Vuelta de Obligado *A chain was placed from Columbus, Kentucky across the

Mississippi River The Mississippi River is the main stem, primary river of the largest drainage basin in the United States. It is the second-longest river in the United States, behind only the Missouri River, Missouri. From its traditional source of Lake Ita ...

Missouri Missouri (''see #Etymology and pronunciation, pronunciation'') is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. Ranking List of U.S. states and territories by area, 21st in land area, it border ...

in order to block Union ships during the

American Civil War The American Civil War (April 12, 1861May 26, 1865; also known by Names of the American Civil War, other names) was a civil war in the United States between the Union (American Civil War), Union ("the North") and the Confederate States of A ...

*Between the in Mugardos and , in ria of Ferrol, to defend the city and naval base.

Notes

:A. Some sources have the chain being dismantled instead of broken by a ship in the siege of Damietta and in the

References

{{Authority control Nautical terminology