in 1875 a prison was built near Borstal for convicts employed in constructing the seven proposed forts. The design of the forts underwent change. Caponiers in the ditch were abandoned in favour of counterscarp galleries in the angles of the ditch. The four southern forts of Borstal, Bridgewoods, Horsted and Luton were begun first. There was a hiatus in construction during the 1880s and Borstal was completed in the mid 1890s. During the First World War the fort was used as barrack accommodation and stores preparatory to movement to the Western Front. Just prior to the Second World War, four 4.5in AA guns were installed in concrete emplacements and a large hutted camp was constructed to the rear of the fort to house gun crews and ATS personnel. A light railway was constructed alongside the emplacements to supply ammunition to the guns. In 1961 the fort passed to the Home Office and the Borstal Institution used it as a store and pigsty. It has since passed into private hands.