Boom (navigational barrier)

Navigational barrier

For other uses, see Boom.

A boom blocking the River Foyle during the siege of Derry

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.[1]

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.[2][3]

## Description

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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

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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.[2] 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.[4]

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.[5][6][7][8]A Frequently, however, attackers instead seized the defences and cut the chain or boom by more conventional methods. The boom at the siege of Derry, 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 batteries, or forts. In the Age of Sail, 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

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* Crusaders break a chain protecting the harbour (at left) in the siege of Damietta.

* Boom towers in Norwich

* Remains of the great chain that protected the Golden Horn

* A preserved section of the Hudson River Chain

* Remains of the Shoeburyness Boom, built to protect the Thames Estuary from Soviet submarines during the Cold War

## Examples

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### Historical

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Defensive system for Ferrol, Spain, which proved to be useful against the Ferrol Expedition.

* The entrance to the Cothon at Carthage was protected by a chain.
* 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 to Missouri in order to block Union ships during the American Civil War[9]
* Between the A Palma Castle [gl] in Mugardos and Saint Philip Castle [gl], in ria of Ferrol, to defend the city and naval base.

## See also

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Wikimedia Commons has media related to Defensive booms.

* Anti-submarine net
* Boom defence vessel \- a vessel charged with laying anti-submarine nets
* Log boom \- a boom for collecting logs
* Boom (containment) \- a boom for containing oil spills
* Pile barrage \- an underwater fortification consisting of piles driven into the sea or river bed

## Notes

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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

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1. ^ Anders Högmer (1998). "Sjöfartspärrar och Östergötlands hövdingadöme". abc.se. Marinarkeologi. Retrieved 2025-02-14.
2. ^ a b Philip Davis (May 7, 2012). "Site types in the Gatehouse listings — Chain Tower". Gatehouse. Retrieved October 17, 2013.
3. ^ Boom Towers, Norwich
4. ^ Bob Hind (January 27, 2013). "Filling in the missing links on history of harbour chain". The News. Archived from the original on October 21, 2013. Retrieved October 17, 2013.
5. ^ Gibbon, Edward. The History of the Decline and Fall of the Roman Empire, Volume 6. p. 510.
6. ^ "THE DUTCH IN THE MEDWAY - 1667". M.A. de Ruyter Foundation. Archived from the original on October 21, 2013. Retrieved October 21, 2013.
7. ^ Hervey, Frederic (1779). The Naval History of Great Britain: From the Earliest Times to the Rising of the Parliament in 1779. W Adlard. pp. 77.
8. ^ Long, WH (2010). Medals of the British Navy and How They Were Won. Great Britain: Lancer Publishers. p. 24\. ISBN 9781935501275.
9. ^ "The Mississippi River in the Civil War Historical Marker".

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