the 1850s caused a further invasion scare, and a Royal Commission was set up in 1859 to investigate the defences of Britain. As a result, more work was deemed necessary at the Heights, and the Drop Redoubt had its defences improved. Caponiers were added to four of the corners of the existing fort (each with a stone staircase leading up to the top of the Redoubt), and gunrooms were built alongside two of them to allow fire along the North and South-East Lines. The original magazine was enlarged, and covered with a large earth bank as protection from mortar-fire. The Officers’ Quarters, Guardroom, and cells also date from this period. They can be distinguished from the earlier work by the semi-circular shape of their arches. During World War II, the Redoubt housed a squad of commandos that, in the event of invasion, would have been responsible for destroying Dover Harbour. Their presence was secret and the lines around the Redoubt were mined. Evidence of their stay are the sally ports in Caponiers 1 & 2, and the short tunnel leading from the encircling line to Drop Redoubt Road. The entrance to Drop Redoubt was via a bridge. The inner third of this was pivoted so that the Redoubt could be isolated. The pivot and the recess into which the bridge swung can still be seen, although the bridge has long since gone. In the 1980s, a temporary scaffolding bridge was built by the army to enable access for guided tours of the Redoubt, but this was removed in the middle 1990s to prevent unauthorised entry and vandalism. The Armaments Originally, the Redoubt was to be equipped with 12 smooth bore 24-pounder guns and two carronades. However, it is unlikely that many were installed since the Napoleonic War was almost over by the time construction was completed. In 1851, only three 24-pounders were in place, with six 12-pounder saluting guns and an 8" mortar. Following the Second Period, eleven Armstrong 64-pounder Rifled Breech Loaders were installed on traversing carriages. These proved unsatisfactory and a return was made to muzzle loaders. The artillery at the Redoubt faced mostly inland; it was intended to attack an invading force attempting to capture Dover from the rear. Earthworks, bastions and gates As part of the first rebuilding, from 1804 onwards, a series of earthworks (ramparts and ditches) were constructed: the North Lines, running along the