The Twydall Profile was a style of fortification used in British and Imperial polygonal forts at the end of the 19th century. The sloping earthworks employed in the Twydall Profile were intended to be quick and inexpensive to construct and to be effective in the face of the more powerful artillery and high explosive ammunition being introduced at that time. The name comes from the village of Twydall in Kent, where the first forts of this type were built.
The design of the Twydall Profile emerged following the Siege of Plevna during the Russo-Turkish War of 1877 to 1878. There, the hastily constructed Turkish fieldworks had successfully withstood repeated Russian assaults between July and September 1877; the Russians finally took the town after defeating an attempted Turkish breakout in December. The reason for the effectiveness of the Turkish defences was attributed to two factors; firstly, the force of the Russian shells had been absorbed by the Turkish earthworks and secondly, the defenders had been armed with American breech loading and repeating rifles and had been able to break up the attacking infantry formations before they had reached their objectives. [1]
In the United Kingdom, a huge investment had been made in the previous decades in a considerable number of large fortifications to defend the naval dockyards, collectively known as the Palmerston Forts. Not only had many of these been designed to mount artillery which was now obsolete, but the intended defensive scheme for the dockyard at Chatham in Kent had never been completed. The solution devised and promoted by the forward-thinking military engineer, Lieutenant-Colonel Sir George Sydenham Clarke, was for a smaller, less expensive type of fort or redoubt, which could be manned by infantry and mobile field artillery rather than large guns fixed in deep emplacements. Previous forts had relied on defence against an infantry attack using a deep ditch with steep walls, often revetted with stone, brick, or concrete, known as the scarp (facing outwards) and the counterscarp (facing inwards). The fort was further protected by caponiers and counterscarp galleries; positions from which rifle or light artillery fire could be directed along the ditch. In the proposed new redoubts, all of this would be replaced by sloping earth banks, intended to maximise the effect of the defenders' rifles and minimise the effect of the attackers' artillery.
In 1885, a pair of small forts were accordingly built by way of an experiment, designed to protect the eastern overland approaches to Chatham, near the village of Twydall. Woodlands Redoubt and Grange Redoubt were collectively known as the Twydall Redoubts and were intended to prove the effectiveness of the new system and how quickly and cheaply they could be constructed. Under the direction of Sir Andrew Clarke, the Inspector-General of Fortifications, [2] Woodlands Fort was built by a civilian contractor within a month, for the sum of £1,800. Grange Fort was built by the Royal Engineers. Sir Andrew reported that the full cost of the project was "...£6,000 as opposed to at least £45,000 for the old type [of fort]". The redoubts each had a central row of bomb-proof casemates in which the infantry garrison could shelter and was surrounded by a low earthen rampart, on which field guns could be sited and a banquette or fire step and parapet, over which the infantry could fire their rifles. The shallow ditch was crossed by a drawbridge at the rear; however, neither work had the barracks, fixed artillery emplacements, magazines, or caponiers that might have been expected in a fort of this period. [3]
In the study of fortification, the term "profile" means the form of a defensive structure when viewed as a cross section in the vertical plane. [4] The Twydall Profile consists of a simple earthen rampart, built as low as possible; between 10 and 15 feet (3.0 and 4.6 metres) and not greater than 20 feet (6.1 metres) was recommended. From the crest of the rampart continuous gentle slope, ideally of a gradient of 1 in 10, falling to 15 or 20 feet (4.6 or 6.1 metres) below the original surface of the ground. At the foot of the slope is an unclimbable palisade made of angled steel palings, often referred to as a "Dacoit fence", recommended to be 9 feet 6 inches (2.90 metres) tall. Beyond that, there is a steep earth counterscarp, the main function of which is to protect the palisade from artillery fire. Entanglements of barbed wire may be sited on the forward slope of the rampart and on the crest of the counterscarp. The frontal slope of the rampart, known as the "superior slope", was recommended ideally to be of a gradient of 1 in 10, which had been shown in tests to cause the majority of incoming shells to ricochet on impact. [5]
Newhaven Fort is a Palmerston fort built in the 19th century to defend the harbour at Newhaven, on the south coast of England. It was the largest defence work ever built in Sussex and is now open as a museum.
Shoreham Redoubt is a historical military defensive structure and scheduled monument at the entrance to Shoreham harbour, at the mouth of the River Adur in West Sussex, England. It was planned in the 1850s during a period of political alarm in the United Kingdom. Construction of the fort was completed in June 1857 at a cost of £11,685. The design is similar to that of Littlehampton Fort, which had been built in 1854.
The Western Heights of Dover are one of the most impressive fortifications in Britain. They comprise a series of forts, strong points and ditches, designed to protect the country from invasion. They were created in the 18th and 19th centuries to augment the existing defences and protect the key port of Dover from both seaward and landward attack; by the start of the 20th century Dover Western Heights was collectively reputed to be the 'strongest and most elaborate' fortification in the country. The Army finally withdrew from the Heights in 1956–61; they are now a local nature reserve.
Fort Luton was built between 1876 and 1892 south of Chatham, Medway, South East England. It is one of the five late Victorian land front forts built to defend the overland approaches to Chatham. It is the smallest of the Chatham forts and was built near to the village of Luton.
Beacon Hill Battery is a late-19th and 20th century coastal fortification that was built to defend the port of Harwich, Essex. It is a scheduled ancient monument.
Crownhill Fort is a Royal Commission Fort built in the 1860s in Crownhill as part of Lord Palmerston's ring of land defences for Plymouth. Restored by the Landmark Trust, it is now home to several small businesses, museums, exhibitions and a holiday apartment sleeping up to eight people. The Fort is open to the public on the last Friday of each month and hosts tours for local schools and societies at other times.
Fort Fareham is one of the Palmerston Forts, in Fareham, England. After the Gosport Advanced Line of Fort Brockhurst, Fort Elson, Fort Rowner, Fort Grange and Fort Gomer had been approved by the Royal Commission on the Defence of the United Kingdom a decision was made to build an outer line of three more forts two miles in advance of the Gosport Advanced Line. Of these three projected forts only Fort Fareham was built due to the need to cut costs. It acted as a hinge between the forts on Portsdown Hill and those of the Gosport Advanced Line, filling the gap at Fareham. It has been a Grade II Listed Building since 1976.
A caponier is a type of defensive structure in a fortification. Fire from this point could cover the ditch beyond the curtain wall to deter any attempt to storm the wall. The word originates from the French caponnière, meaning "chicken coop".
Fort Brockhurst is one of the Palmerston Forts, in Gosport, England, and a Scheduled Ancient Monument. It is now an English Heritage property.
Farningham is a village and civil parish in the Sevenoaks District of Kent, England. It is located 3 miles (5 km) south-east of Swanley. It has a population of 1,314.
A scarp and a counterscarp are the inner and outer sides, respectively, of a ditch or moat used in fortifications. Attackers must descend the counterscarp and ascend the scarp. In permanent fortifications the scarp and counterscarp may be encased in stone. In less permanent fortifications, the counterscarp may be lined with paling fence set at an angle so as to give no cover to the attackers but to make advancing and retreating more difficult.
The Séré de Rivières system was named after Raymond Adolphe Séré de Rivières, its originator. The system was an ensemble of fortifications built from 1874 along the frontiers and coasts of France. The fortresses were obsolescent by 1914 but were used during the First World War.
In military engineering, a ditch is an obstacle designed to slow down or break up an attacking force, while a trench is intended to provide cover to the defenders. In military fortifications the side of a ditch farthest from the enemy and closest to the next line of defence is known as the scarp while the side of a ditch closest to the enemy is known as the counterscarp.
Fort Rowner is one of the Palmerston Forts, in Gosport, England.
The Fort des Ayvelles, also known as the Fort Dubois-Crancé, is a fortification near the French communes of Villers-Semeuse and Les Ayvelles in the Ardennes, just to the south of Charleville-Mézières. As part of the Séré de Rivières system of fortifications, the fort was planned as part of a new ring of forts replacing the older citadel of Mézières with dispersed fortifications. With advances in the range and destructive power of artillery, the city's defensive perimeter had to be pushed away from the city center to the limits of artillery range. The Fort des Ayvelles was the only such fortification to be completed of the ensemble, as resources were diverted elsewhere. At the time of its construction the fort controlled the Meuse and the railway line linking Reims, Montmédy, Givet and Hirson. The Fort des Ayvelles was reduced in status in 1899, its masonry construction rendered obsolete by the advent of high-explosive artillery shells. However, it was re-manned for the First World War before it was captured by the Germans on 29 August 1914. The fort was partly destroyed in 1918. During the Battle of France in 1940 the fort was bombarded. French resisters were executed at Ayvelles during both world wars. At present the fort is maintained by a preservation society, and may be visited.
A Carnot wall is a type of loop-holed wall built in the ditch of a fort or redoubt. It takes its name from the French mathematician, politician, and military engineer, Lazare Carnot. Such walls were introduced into the design of fortifications from the early nineteenth century. As conceived by Carnot they formed part of an innovative but controversial system of fortification intended to defend against artillery and infantry attack. Carnot walls were employed, together with other elements of Carnot's system, in continental Europe in the years after the final defeat of Napoleon in 1815, especially by the Prussians, other Germans and Austrians. Their adoption was initially resisted by the French themselves and by the British.
Woodland Fort is a Royal Commission Fort built in the 1860s as part of Lord Palmerston's ring of land defences for Plymouth, England. Currently owned by Plymouth City Council, the site is in use but largely derelict.
Camden Fort Meagher is a coastal defence fortification close to Crosshaven, County Cork, Ireland. Together with similar structures at Fort Mitchell, Fort Davis (Whitegate), and Templebreedy Battery, the fort was built to defend the mouth of Cork Harbour. Though originally constructed in the 16th century, the current structures of the fort date to the 1860s. Originally named Fort Camden and operated by the British Armed Forces, the fort was handed-over to the Irish Defence Forces in 1938. Renamed Fort Meagher in honour of Thomas Francis Meagher, it remained an Irish military installation until 1989 when the Irish Army handed the fort over to Cork County Council. It remained largely overgrown until 2010 when a group of local volunteers began restoration and development of the fort for heritage and tourism purposes. The fort was renamed Camden Fort Meagher and is now open seasonally to visitors, with exhibits on the fort's Brennan torpedo installation.
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