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. 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 An anti-submarine net or anti-submarine boom is a boom placed across the mouth of a harbour or a strait for protection against submarines. Examples of anti-submarine nets * Lake Macquarie anti-submarine boom * Indicator net * Naval operations in ...

. 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 t ...

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 a first attempt against the town by Jacobite forces on 7 December 1688 that was foiled when 13 apprentices shut the gates ...

, 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 boa ...

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

artillery Artillery is a class of heavy military ranged weapons that launch munitions far beyond the range and power of infantry firearms. Early artillery development focused on the ability to breach defensive walls and fortifications during siege ...

batteries, or forts. In the Age of Sail, a boom protecting a harbour could have several ships defending it with their

broadside Broadside or broadsides may refer to: Naval * Broadside (naval), terminology for the side of a ship, the battery of cannon on one side of a warship, or their near simultaneous fire on naval warfare Printing and literature * Broadside (comic ...

s, 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 Norfolk, England, of which it is the county town. Norwich is by the River Wensum, about north-east of London, north of Ipswich and east of Peterborough. As the seat of the See of Norwich, with ...

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

Golden Horn The Golden Horn ( tr, Altın Boynuz or ''Haliç''; grc, Χρυσόκερας, ''Chrysókeras''; la, Sinus Ceratinus) is a major urban waterway and the primary inlet of the Bosphorus in Istanbul, Turkey. As a natural estuary that connects with t ...

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

Hudson River Chain The Hudson River Chains were a series of chain booms constructed across the Hudson River at West Point by Continental Army forces from 1776 to 1778 during the American Revolutionary War. These served as defenses preventing British naval vessels ...

File:Shoebury Boom - geograph.org.uk - 915365.jpg, Remains of the

Shoeburyness Boom The Shoeburyness Boom (also known as the Sheerness Boom, Thames Boom or Thames Estuary Boom) refers to two successive defensive barriers across most of the Thames Estuary in the mid-20th century. As to the part perpendicular to the north shor ...

, 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 salini ...

from Soviet submarines during the

Cold War The Cold War is a term commonly used to refer to a period of geopolitical tension between the United States and the Soviet Union and their respective allies, the Western Bloc and the Eastern Bloc. The term '' cold war'' is used because the ...

Examples

Historical

*The chain at

Fort Blockhouse Fort Blockhouse is a military establishment in Gosport, Hampshire, England, and the final version of a complicated site. At its greatest extent in the 19th century, the structure was part of a set of fortifications which encircled much of Gos ...

, 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 i ...

from 1431 to 1539. *The

Leonine Wall Leonine may refer to: Lions * Leonine facies, a face that resembles that of a lion Popes Leo * Leonine City, a part of the city of Rome * Leonine College, a college for priests in training, in Rome, Italy * Leonine Prayers, a set of prayers tha ...

included a chain blocking the

Tiber The Tiber ( ; it, Tevere ; la, Tiberis) is the 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 Riv ...

*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, East 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 the ...

*The chain blocking the Parana River during the

Battle of Vuelta de Obligado The naval Battle of Vuelta de Obligado took place on the waters of the Paraná River on 20 November 1845, between the Argentine Confederation, under the leadership of Juan Manuel de Rosas, and a combined Anglo-French fleet. The action was part o ...

*A chain was placed from

Columbus, Kentucky Columbus is a home rule-class city in Hickman County, Kentucky, in the United States. The population was 170 at the 2010 census, a decline from 229 in 2000. The city lies at the western end of the state, less than a mile from the Mississippi Ri ...

across the

Mississippi River The Mississippi River is the second-longest river and chief river of the second-largest drainage system in North America, second only to the Hudson Bay drainage system. From its traditional source of Lake Itasca in northern Minnesota, it f ...

Missouri Missouri 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 is bordered by eight states (tied for the most with Tennessee ...

in order to block Union ships during the

American Civil War The American Civil War (April 12, 1861 – May 26, 1865; also known by other names) was a civil war in the United States. It was fought between the Union ("the North") and the Confederacy ("the South"), the latter formed by states th ...

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