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  • Fixed harbour defences

Fixed harbour defences are ground installations used in time of war to defend harbours and ports from attack by sea. In the past, the attack might come from Viking ships, pirate ships or naval ships. In the 20th century the attack could also come from submarines, planes or missiles.

Some examples of fixed harbour defences are fortified structures protecting personnel and providing a platform for devices that hurl missiles; underground bunkers protecting supplies, power generators and control rooms; defensive barriers across the harbour entrance; and arrays of mines on the seabed of the harbour which can be selectively triggered from the shore. By contrast, some examples of harbour defences which are mobile, and not fixed, are fire ships, harbour defense launches, dive bombers, and infantry or tank divisions.

Apart perhaps from the use of deep bunkers, traditional fixed harbour defences are not used these days. Modern missile and monitoring systems, with their long range and pin point targeting capabilities, render traditional fixed defences irrelevant.

Contents

[edit] History

The Roman Empire fortification system of the Saxon Shore at the end of the 3rd century
The Roman Empire fortification system of the Saxon Shore at the end of the 3rd century
Siege of Constantinople
Siege of Constantinople

[edit] Fortifications and barriers

The classic fixed harbour defence was the fort. Towards the of the 3rd century the Roman Empire established a network of mainly coastal fortifications on both sides of the English Channel. This defence system, called the Saxon Shore, defended many harbours, possibly from seaborne piracy.

During the 885-886 Siege of Paris, the Franks built fortified bridges to defend the Seine; unable to progress past these, the Vikings created fire ships by filling three warships with combustible material and pulled them upriver in a failed attempt to destroy them. [1]

Many coastal forts incorporated harbour facilities which enabled supply from the sea in times of land siege. Some castles, such as Conwy, had projecting spurs with towers acted as breakwaters as well as defensive structures.[2]

By the later medieval period it was customary for towns on the coast or navigable rivers to defend their harbours and waterways by chains or booms; this also facilitated the collection of tolls.[3] These could be operated by windlasses or pulleys located in boom towers.[4] At Harfleur, at the 1415 siege during the Hundred Years' War, the port's iron chain defences were supplemented by sharpened stakes driven into the riverbed.[5]

The 15th century writer Gutierre Diaz de Gamez recorded an attack on Marseilles in 1404:

"A strong chain of iron closes or frees the [harbour] entrance, which is very narrow. This chain is riveted to a great lighthouse in the middle of the harbour, so that no ship can come in or go out without leave.[6]

Diaz de Gamez goes on to describe a signal staff on an island just off shore; it was fitted with two sails, one the square sail from a ship, the other a triangular sail from a galley. A lookout keeps watch and when he spies a boat, he lowers the relevant sail to warn the town when a ship approaches.[6]

[edit] Catapults and Greek fire

This possibly anachronistic lithograph from an 1869 Harper's Magazine depicts a 13th century engine for throwing Greek fire in a barrel.
This possibly anachronistic lithograph from an 1869 Harper's Magazine depicts a 13th century engine for throwing Greek fire in a barrel.

Fortifications provided protection for infantry or calvary, and also provided protected platforms for devices that could hurl things at naval boats. Siege catapults were used in 400-300 BC, both in China[7] and Greece[8]

Later medieval designs included improved siege weapons which could be used against naval boats. The catapult evolved through the mangonel, onager, ballista to the powerful counterweight trebuchet. The trebuchet was first developed in China in the 3rd century BC as a traction machine. It was brought to Europe in the 4th century AD. In the twelfth century the much improved counterweight trebuchet appeared in both Christian and Muslim lands around the Mediterranean . This powerful machine could fling three-hundred-pound (140 kg) projectiles at high speed with far more accuracy than previous catapults.

Catapults could hurl rocks, burning sand, or fire pots that created a fireball on impact. In the 7th century the Byzantines invented Greek fire. A combustible liquid, it could be shot from siphons or catapults, and it burst into flames on impact. It burned on water, and was used effectively against naval boats.[9]

Greek fire was successfully used during the crusades by the Turks in 718 to defeat a naval force during the Siege of Constantinople. It was was probably first used in Western Europe in the 12th century.[10] Various versions seem to have existed, and the recipes were frequently kept secret; experts today still debate the exact composition, although some recipes are known.[11]

[edit] Cannon

Aerial view of Fort Jefferson
Aerial view of Fort Jefferson

After the introduction of artillery in the 14th century, Then cannon were added in the 14th century gunpowder

In China, the 13th century saw the beginnings of rocketry[12][13] and the manufacture of the oldest gun still in existence,[14][15] a descendant of the earlier fire-lance, a gunpowder-fueled flamethrower that could shoot shrapnel along with fire. The Huolongjing text of the 14th century also describes hollow, gunpowder-packed exploding cannonballs.[16]


The first documented use of artillery using gunpowder occurred in 1132 when the Chinese general Han Shizhong used huochong to capture a city.

In 1331, the Spanish historian Zurita recorded a "new machine that caused great terror. It threw iron balls with fire."[17]

Cannon certainly saw its first real use on the European battlefield during the Hundred Years War, being only used in small numbers by a few states during the 1340s.

The first definite use of artillery in the region was against the Ottoman siege of Constantinople, in 1396, forcing the Ottomans to withdraw.[18]

Gunpowder had also made the formerly devastating Greek fire obsolete, and with the final fall of what had once been the strongest walls in Europe on May 29, "it was the end of an era in more ways than one".[19]

Toward the end of the Middle Ages, the development of cannon made revolutionary changes to siege warfare throughout Europe, with many castles becoming susceptible to artillery fire. The primary aims in castle wall construction were height and thickness, but it became almost impossible to follow this ideal against ever more powerful cannon. Inevitably, those fortifications previously deemed impregnable, eventually proved inadequate in the face of gunpowder. The general adoption of cannon led to the loss of importance of majestic towers and merlons. Walls of new fortresses were thicker and angulated, while towers became lower and stouter.


Cannon influenced the way fortifications were constructed. Machiavelli wrote in The Art of War: "There is no wall, whatever its thickness that artillery will not destroy in only a few days". Although castles were not immediately made obsolete by cannon, their importance declined.[20] The walls of new fortresses were thicker, and towers became lower and stouter.[20] Increasing use was made of earthen, brick and stone breastworks and redoubts. These soon replaced traditional castles in Europe, and eventually castles in the Americas were superseded by bastions and forts.[21]


In England, significant changes were evident from the 16th century, when Henry VIII began building the Device Forts between 1539 and 1540 as artillery fortresses. They were built by the state at strategic points for the first powerful cannon batteries, such as Deal Castle, which was perfectly symmetrical, with a low, circular keep at its centre. Over 200 cannon and gun ports were set within the walls, and the fort was essentially a firing platform, with a shape that allowed many lines of fire; its low curved bastions were designed to deflect cannon balls.[22]



[edit] 20th century

HMS Formidable passing through the anti-submarine boom in Sydney Harbour in 1945
HMS Formidable passing through the anti-submarine boom in Sydney Harbour in 1945

By the 20th century...

Submarine defences There are five fixed defenses used in detecting a submarine attempting to enter a harbor:

  • The indicator loop
  • The controlled mine loop
  • The harbor defense listening gear
  • The indicator net
  • Supersonic set for boom gate vessels

Fortified batteries are sometimes set up well outside the harbour limits, on outlying islands or distant headlands. These can provide a more effective defence of the harbour by engaging enemy intruders long before they can range their guns on the harbour itself.


Likewise, minefield can sometimes effectively defend a harbour from positions well outside the harbour limits.

Some harbours are anchorages for naval fleets, eg Scapa Flow and Fort Jefferson, located on a strategic island in the Florida Keys.


[edit] Artillery

Include Searchlight batteries and Anti-aircraft artillery batteries:



[edit] Barriers and booms

Use of chains. Sunken block ships. Churchil barrier. placing a defensive chain or boom or net across the harbour entrance

Beach defences

  • Obstructions
  • Pill boxes (machine gun nests)


[edit] Sensing devices

  • lookout : visual sensing. Observation centres, binoculars.
  • nighttime - searchlights
  • Hydrophonic listening device
  • magnetic sensing-indicator loops
  • radar installations

Fixed harbour sensing: the use of lookout stations, manned by personnel perhaps scanning the horizon with binoculars. the use of fixed hydrophonic listening devices or radar installations. indicator loop

  • the hydrophone

relied on an operator listening for the unique sounds made by a submarine’s engine. It could be used as part of a fixed shore-based defensive system or dangled over the side of a drifting ship. By late 1918 the British had established 21 hydrophone stations around the coast while also equipping several thousand vessels of the auxiliary patrol. Hydrophones began as non-directional instruments, but even the relatively sophisticated directional hydrophone could give no indication of a target’s range. A more fundamental weakness, however, was that as a passive system, detection depended on an indiscreet target. By using slow speed, quiet routines, and insulating the machinery from the hull, a skilful submarine commander could minimise his chances of discovery. Indeed, despite the success attributed to hydrophones during the war, later research found that of the U-boats sunk by the auxiliary patrol, only one had been heard before sighting.13 The second device was another passive system, and made use of indicator cables laid on the seabed and connected in turn to a shore station. The loop system, as it was known, worked by detecting the electro-magnetic disturbance caused by the passage of a submarine’s steel hull above the cable, and displaying this variation on a continuous trace in the operating station. Although almost impossible for a submarine to evade, the system was only suitable for fixed harbour defences.

Consequently, the Admiralty placed most hope in the last detection device, commonly known by its acronym ‘asdic’. Similar to a hydrophone, an asdic made use of underwater acoustics, but was based on high frequency echo ranging, and hence was an active rather than a passive sensor system. It could be fitted as part of a harbour defence, but the Navy expected asdic’s prime application to be in surface vessels. The device consisted of an oscillator built

[23]

[edit] Indicator loops

The indicator loop was another sensing device. It was developed in great secrecy during World war I at/by...

The indicator loop is a warning device, but the controlled mine loop provides a lethal weapon as well as a warning device. Both are operated by magnetic influence. They will probably be de-energized while channel is being swept by magnetic sweeps as the magnetic sweeps interfere with the detector instruments. Harbor defense listening gear consists of sensitive elements mounted on the sea bottom and controlled from the shore. Indicator nets offer no definite obstacle, but give visual notice of the presence of submarines. Supersonic sets for the boom gate vessels are for the purpose of preventing an entry into a protected harbor when it is opened for the entry of friendly ships.[24]

Apart from normal harbour defences such as guns and searchlights, fixed anti-submarine defences included indicator loops which gave an indication that a vessel had passed over a predetermined line; harbour defence asdics which required skilled operation; controlled mines which were exploded by a shore operator as a submarine crossed the line; and anti-submarine booms. All these required large quantities of expensive material and, with the possible exception of the asdics, could be installed only from specially equipped vessels.[25]

[edit] Controlled minefields

In practical terms, the Admiralty envisaged a layered defence based on three different devices.

Scapa Flow Churchill Barriers


Siege weapons are now considered obsolete owing to the effectiveness of aircraft-delivered munitions and cruise missiles, which have made defensive area fortifications obsolete. The only cost effective static defensive structures are now deep bunkers used for military command and control. Even these fixed assets are of questionable value as it appears that the most survivable command and control of mobile defensive forces (such as modern tactical and strategic aircraft, mechanized cavalry and mechanized infantry) is through decentralized command and the use of mobile command centers.


[edit] When harbour defences fail

The bombardment of Alexandria (1882)
The bombardment of Alexandria (1882)
An oil tank explodes during a Japanese air raid on Darwin in 1942.
An oil tank explodes during a Japanese air raid on Darwin in 1942.

[edit] See also


  • There is no evidence for the use of stone-throwing machines aboard ships.[26]

[edit] Notes

  1. ^ Bennett et al, pp 221-222
  2. ^ Creighton and Higham, p 99
  3. ^ Creighton and Higham, pp 40-41
  4. ^ Creighton and Higham, p 118
  5. ^ Kaufmann and Kaufmann, p 151
  6. ^ a b Diaz de Gamez, p 60
  7. ^ Liang (2006)
  8. ^ Rihall (2007)
  9. ^ Kaufmann & Kaufmann, p 61
  10. ^ Bradbury, p 302
  11. ^ Nossov, pp 196-8
  12. ^ Crosby 2002:100–103
  13. ^ Needham 1986:12
  14. ^ Chase 2003:130
  15. ^ Needham 1986:293–294
  16. ^ Needham, Volume 5, Part 7, 264.
  17. ^ Partington, J. R., A History of Greek Fire and Gunpowder, reprint by Johns Hopkins University Press, p. 191 (Latin text of Zurita)
  18. ^ Turnbull, Stephan (2004). The Walls of Constantinople AD 324–1453 (Fortress 25). Osprey Publishing. ISBN 1-84176-759-X. 
  19. ^ Stephen Turnbull, The Walls of Constantinople, AD 324–1453, Osprey Publishing, 2004. ISBN 1-84176-759-X.
  20. ^ a b Wilkinson, p 81
  21. ^ Chartrand, Spanish Main 1492-1800
  22. ^ Wilkinson, Castles (Pocket Guides).
  23. ^ [www.navy.gov.au/spc/maritimepapers/piama15/piama15_ch3.pdf Frustrations and Failures 1919-30, Page 3]
  24. ^ [http://www.history.navy.mil/library/online/ss-doc-5.htm Submarine defensive measures
  25. ^ NZ Anti-Submarine Policy
  26. ^ Bennett et al, p 241

[edit] References

  • Bennett, Matthew; Bradbury, Jim; DeVries, Kelly; Dickie, Iain; Jestice, Phyllis G. (2005) Fighting Techniques of the Medieval World: AD 500-AD 1500, London: Amber Books ISBN 1-86227-299-9
  • Bradbury, Jim; (2004) The Routledge Companion to Medieval Warfare, London: Routledge, ISBN 0415221269
  • Creighton, Oliver; Higham, Robert; Medieval Town Walls: An Archeology and Social History of Urban Defence, UK; Tempus, 2005, ISBN 0752414453
  • Diaz de Gamez, Gutierre; The Unconquered Knight: a Chronicle of the Deeds of Don Pero Nino, Count of Buelna, written 1431-49, translated by Joan Evans, UK: The Boydell Press, 2004 ISBN 1843831015
  • Kaufmann, J.E.; Kaufmann, H.W.; The Medieval Fortress: Castles, Forts and Walled Cities of the Middle Ages, UK: Greenhill Books, 2001, ISBN 1853674559
  • Nossov, Konstantin; Ancient and Medieval Siege Weapons, UK: Spellmount Ltd, 2006, ISBN 186227343X
  • Liang, Jieming (2006). Chinese Siege Warfare: Mechanical Artillery & Siege Weapons of Antiquity. ISBN 981-05-5380-3. 
  • Rihall, Tracy (2007) The Catapult: A History
  • Turnbull, Stephen (2004). The Walls of Constantinople AD 324–1453 (Fortress 25). Osprey Publishing. ISBN 1-84176-759-X. 
  • Needham, Joseph (1986), Science & Civilisation in China, vol. V:7: The Gunpowder Epic, Cambridge University Press, ISBN 0521303583 .
  • Chase, Kenneth (2003), Firearms: A Global History to 1700, Cambridge University Press, ISBN 0521822742 .
  • Wilkinson, Philip. Castles (Pocket Guides). Publisher: DK CHILDREN; Pocket edition (September 29, 1997). ISBN 0789420473. ISBN 978-0789420473


[edit] External links