Twydall Profile

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, that the force of the Russian shells had been absorbed by the Turkish earthworks and secondly, that 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.

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 by means of 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.

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