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. 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 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 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. 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 sieg ...

batteries, or forts. In the

Age of Sail The Age of Sail is a periodization, period that lasted at the latest from the mid-16th century, 16th (or mid-15th century, 15th) to the mid-19th century, 19th centuries, in which the dominance of sailing ships in globalization, global trade and ...

, 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 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 Episcopal see, See of ...

File:Chain Bosphorus.JPG, Remains of the great chain that protected the Golden Horn File:The Great Chain Today.jpg, A preserved section of the Hudson River Chain File:Shoebury Boom - geograph.org.uk - 915365.jpg, Remains of the Shoeburyness Boom, built to protect the Thames Estuary from Soviet submarines during the Cold War

Examples

Historical

*The chain at Fort Blockhouse, protecting Portsmouth Harbour from 1431 to 1539. *The Leonine Wall included a chain blocking the Tiber *A chain spanned the Golden Horn *A chain and boom blocked the River Medway during the Raid on the Medway * Hudson River Chain *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 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 ...

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 state ...

Notes

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

References

{{Authority control Nautical terminology