THE TWYDALL PROFILE
The Twydall Profile was developed by the British Military towards the end of the 19th Century and was then used for coastal defence batteries and other fixed defences. For an overview of the evolution of British fortifications during the artillery age, see here.
The success of Turkish field defences in withstanding the Russian attacks between 1877 and 1878 showed how effective earth ramparts were against the modern high velocity rifled guns. The concept of low-profile emplacements set in well concealed positions with primarily earthen ramparts was developed in part from this these Turkish fortifications. Infantry armed with modern rifles and supported by mobile artillery could be expected to hold earth work fortifications against enemy attacks.
This was a move away from the old brick and concrete fortifications of the 1860s to 1880s towards a lower profile position using earth as the principle building material. The introduction of smokeless propellants and breech loading guns, meant that the visibility of gun batteries was substantially reduced when compared with the old black powder days. Bolt loading rifles and machine guns enabled infantry in prepared positions to repel attackers without the need for moats, counter scarp galleries and caponiers.
In 1885 two redoubts were built near the village of Twydall in Kent incorporating these new concepts. One was built by a civilian contractor and the other by the Royal Engineers. Both were built at about a tenth of the cost of a conventional fortification of that time, and the construction time was just over one month. Each Redoubt had an earthen rampart around it which could be used by the defenders to engage an attacker. Bombproof casemates were built to house the troops but there were not fixed gun emplacements. A shallow perimeter ditch, with an unclimbable fence in the bottom, then a belt of wire protection surrounded the redoubt. Entry to the redoubt was over a drawbridge.
The trial was obviously regarded as a success and the concept of the Twydall Profile was adapted for coastal defence batteries and other fortifications. There are numerous examples of coastal defence batteries incorporating the Twydall concept, such as West Blockhouse Battery and East Blockhouse Battery in Milford Haven, Beacon Hill Fort in Harwich and Wolsey Battery in Malta. The circle of London Mobilisation Centres built between 1889 and 1903 as part of the London Defence Scheme; also closely followed the Twydal Profile. These redoubts included underground magazines for the storage of ammunition.