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.
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.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.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.
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A naval mine is a self-contained explosive device placed in water to damage or destroy surface ships or submarines. Unlike depth charges, mines are deposited and left to wait until they are triggered by the approach of, or contact with, any vessel. Naval mines can be used offensively, to hamper enemy shipping movements or lock vessels into a harbour; or defensively, to protect friendly vessels and create "safe" zones. Mines allow the minelaying force commander to concentrate warships or defensive assets in mine-free areas giving the adversary three choices: undertake an expensive and time-consuming minesweeping effort, accept the casualties of challenging the minefield, or use the unmined waters where the greatest concentration of enemy firepower will be encountered.
A dry dock is a narrow basin or vessel that can be flooded to allow a load to be floated in, then drained to allow that load to come to rest on a dry platform. Dry docks are used for the construction, maintenance, and repair of ships, boats, and other watercraft.
Chatham Dockyard was a Royal Navy Dockyard located on the River Medway in Kent. Established in Chatham in the mid-16th century, the dockyard subsequently expanded into neighbouring Gillingham.
Calshot Castle is an artillery fort constructed by Henry VIII on the Calshot Spit, Hampshire, England, between 1539 and 1540. It formed part of the King's Device programme to protect against invasion from France and the Holy Roman Empire and defend Southampton Water as it met the Solent. The castle had a keep at its centre, surrounded by a curtain wall and a moat. Initially heavily armed, it had a garrison of 16 men and as many as 36 artillery guns. The castle continued in use for many years, surviving the English Civil War intact and being extensively modernised in the 1770s. During the 19th century, Calshot Castle was used by the coastguard as a base for combating smuggling. In 1894, however, fresh fears of a French invasion led to it being brought back into use as an artillery fort: a large coastal battery was constructed alongside the older castle and a boom built across Southampton Water, controlled from the castle.
The term Hudson River Chain may refer to either of two chain booms constructed across the Hudson River at West Point by Colonial forces from 1776 to 1778 during the American Revolutionary War. These served as defenses preventing British naval vessels from sailing upriver, and were, along with the Hudson River itself, overseen by the Highlands Department of the Continental Army.
Scuttling is the deliberate sinking of a ship by allowing water to flow into the hull. This can be achieved in several ways—seacocks or hatches can be opened to the sea, or holes may be ripped into the hull with brute force or with explosives. Scuttling may be performed to dispose of an abandoned, old, or captured vessel; to prevent the vessel from becoming a navigation hazard; as an act of self-destruction to prevent the ship from being captured by an enemy force ; as a blockship to restrict navigation through a channel or within a harbor; to provide an artificial reef for divers and marine life; or to alter the flow of rivers.
A blockship is a ship deliberately sunk to prevent a river, channel, or canal from being used. It may either be sunk by a navy defending the waterway to prevent the ingress of attacking enemy forces, as in the case of HMS Hood at Portland Harbour in 1914; or it may be brought by enemy raiders and used to prevent the waterway from being used by the defending forces, as in the case of the three old cruisers HMS Thetis, Iphigenia and Intrepid scuttled during the Zeebrugge raid in 1918 to prevent the port from being used by the German navy.
The siege of Damietta of 1218–1219 was part of the Fifth Crusade in which the Crusaders attacked the Egyptian port city of Damietta. The city, under the control of the Ayyubid sultan al-Kamil, was besieged in 1218 and taken by the Crusaders in 1219.
Torpedo nets were a passive ship defensive device against torpedoes. They were in common use from the 1890s until the Second World War. They were superseded by the anti-torpedo bulge and torpedo belts.
In late May and early June 1942, during World War II, submarines belonging to the Imperial Japanese Navy made a series of attacks on the Australian cities of Sydney and Newcastle. On the night of 31 May – 1 June, three Ko-hyoteki-class midget submarines, each with a two-member crew, entered Sydney Harbour, avoided the partially constructed Sydney Harbour anti-submarine boom net, and attempted to sink Allied warships. Two of the midget submarines were detected and attacked before they could engage any Allied vessels. The crew of M-14 scuttled their submarine, whilst M-21 was successfully attacked and sunk. The crew of M-21 killed themselves. These submarines were later recovered by the Allies. The third submarine attempted to torpedo the heavy cruiser USS Chicago, but instead sank the converted ferry HMAS Kuttabul, killing 21 sailors. This midget submarine's fate was unknown until 2006, when amateur scuba divers discovered the wreck off Sydney's northern beaches.
Upnor Castle is an Elizabethan artillery fort located on the west bank of the River Medway in Kent. It is in the village of Upnor, opposite and a short distance downriver from the Chatham Dockyard, at one time a key naval facility. The fort was intended to protect both the dockyard and ships of the Royal Navy anchored in the Medway. It was constructed between 1559–67 on the orders of Elizabeth I, during a period of tension with Spain and other European powers. The castle consists of a two-storeyed main building protected by a curtain wall and towers, with a triangular gun platform projecting into the river. It was garrisoned by about 80 men with a peak armament of around 20 cannon of various calibres.
HMS Medway was the first purpose-built submarine depot ship constructed for the Royal Navy. She was built by Vickers Armstrong at Barrow-in-Furness during the late 1920s. The ship served on the China Station before the Second World War and was transferred to Egypt in early 1940. Ordered to evacuate Alexandria in the face of the German advance after the Battle of Gazala in May 1942, Medway sailed for Lebanon at the end of June, escorted by a light cruiser and seven destroyers. Her strong escort could not protect her; on 30 June a German submarine torpedoed and sank her.
A net laying ship, also known as a net layer, net tender, gate ship or boom defence vessel was a type of small auxiliary ship.
The Sydney Harbour anti-submarine boom net was an anti-torpedo and submarine defence net that was in Sydney Harbour during World War II. It spanned the entire width of the harbour from Laing Point, Watsons Bay to Georges Head, on the northern side of Sydney Harbour. The boom formed part of the Sydney Harbour defences which also included artillery batteries and patrol boats.
Fremantle Harbour is Western Australia's largest and busiest general cargo port and an important historical site. The inner harbour handles a large volume of sea containers, vehicle imports and livestock exports, cruise shipping and naval visits, and operates 24 hours a day. It is located adjacent to the city of Fremantle, in the Perth metropolitan region.
Coastal defenceand coastal fortification are measures taken to provide protection against military attack at or near a coastline, for example, fortifications and coastal artillery. Because an invading enemy normally requires a port or harbour to sustain operations, such defences are usually concentrated around such facilities, or places where such facilities could be constructed. Coastal artillery fortifications generally followed the development of land fortifications, usually incorporating land defences; sometimes separate land defence forts were built to protect coastal forts. Through the middle 19th century, coastal forts could be bastion forts, star forts, polygonal forts, or sea forts, the first three types often with detached gun batteries called "water batteries". Coastal defence weapons throughout history were heavy naval guns or weapons based on them, often supplemented by lighter weapons. In the late 19th century separate batteries of coastal artillery replaced forts in some countries; in some areas these became widely separated geographically through the mid-20th century as weapon ranges increased. The amount of landward defence provided began to vary by country from the late 19th century; by 1900 new US forts almost totally neglected these defences. Booms were also usually part of a protected harbor's defences. In the middle 19th century underwater minefields and later controlled mines were often used, or stored in peacetime to be available in wartime. With the rise of the submarine threat at the beginning of the 20th century, anti-submarine nets were used extensively, usually added to boom defences, with major warships often being equipped with them through early World War I. In World War I railway artillery emerged and soon became part of coastal artillery in some countries; with railway artillery in coast defence some type of revolving mount had to be provided to allow tracking of fast-moving targets.
Fort Lytton is a heritage-listed 19th century coastal fort in the suburb of Lytton in Brisbane, Queensland, Australia. The name “Fort Lytton” is also used to describe the 1 square mile (2.6 km2) military base that surrounded the fort. Fort Lytton was built in 1880–1882, and operated until 1965. The historic fort is now contained in Fort Lytton National Park. The park is open to the public on most Sundays and public holidays. Guided tours are provided by Fort Lytton Historical Association, a non-profit volunteer organisation.
The Shoeburyness 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 shore most of the latter incarnation remains, and its nearest concrete mooring/patrol point 600 metres south. A 2 km stretch, this is designated a scheduled monument and marks the western edge of MoD Shoeburyness firing range, a restricted area. The rest was taken up in the 1960s.
HMAS Lolita (14) was formerly a luxury motor cruiser, commissioned as a channel patrol boat into and operated by the Royal Australian Navy (RAN) during World War II. She was one of thirteen similar vessels, known to Sydney siders as the 'Hollywood Fleet'.