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A boom blocking the River Foyle during the Siege of Londonderry

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.[1] Booms could be military in nature, with the goal of denying access to an enemy's ships; a modern example is the anti-submarine net. Booms could also be used, especially along rivers, to force passing vessels to pay a toll.[1][2]

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.

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.[1] 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.[3]

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.[4][5][6][7]A Frequently, however, attackers instead seized the defences and cut the chain or boom by more conventional methods. The boom at the siege of Londonderry, 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, 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.

Examples

See also

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

  1. 1.0 1.1 1.2 Philip Davis (May 7, 2012). "Site types in the Gatehouse listings — Chain Tower". Gatehouse. http://www.gatehouse-gazetteer.info/key.html. Retrieved October 17, 2013. 
  2. Boom Towers, Norwich
  3. Bob Hind (January 27, 2013). "Filling in the missing links on history of harbour chain". http://www.portsmouth.co.uk/nostalgia/filling-in-the-missing-links-on-history-of-harbour-chain-1-4726442. Retrieved October 17, 2013. 
  4. Gibbon, Edward. The History of the Decline and Fall of the Roman Empire, Volume 6. p. 510. 
  5. "THE DUTCH IN THE MEDWAY - 1667". M.A. de Ruyter Foundation. http://www.deruyter.org/CHATHAM_Wednesday_12th.html. Retrieved October 21, 2013. 
  6. 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. 
  7. Long, WH (2010). Medals of the British Navy and How They Were Won. Great Britain: Lancer Publishers. p. 24. ISBN 9781935501275. http://books.google.ca/books?id=HSUglhRBzFgC&dq=torbay+chain&source=gbs_navlinks_s. 

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