Castle was seized in 1642 by Parliamentary forces at the start of the first English Civil War between the supporters of King Charles I and Parliament, although its captain, Richard Hippesley, remained in post. The war ended in 1646 but, after the few years of unsteady peace, the Second Civil War broke out in 1648. The Parliamentary navy was based in Kent, protected by the other Henrician castles of Walmer, Deal and Sandown, but by May a Royalist insurrection was under way across the county, and the fleet joined the rebellion. Sandgate and its sister castles were occupied by the Royalists. Parliament defeated the wider insurgency at the Battle of Maidstone at the start of June, however, and then sent a force under the command of Colonel Rich to deal with the Kentish castles. Sandgate was still occupied by the Royalists that August, when Rich sent forces to prevent its garrison intervening to disrupt his assault on Deal and Sandown, but was recaptured soon after. During the interregnum, Hippesley initially continued as captain of Sandgate, until he was replaced in 1653, resulting in complaints from him that he had been unfairly treated and that he was owed money by Parliament. During this period the garrison was increased to include a governor, two corporals, twenty soldiers and three gunners. When Charles II was restored to the throne in 1660, Sandgate and the other Device Forts initially remained at the heart of the south coast defences, but by now their design was antiquated. The garrison was cut back to its pre-war levels, and then reduced further in 1682 to only ten men. Sandgate had fallen into a poor condition, and £200 was assigned in 1663 for the repair of the castle, to be met partially from the proceeds of lands around Sandgate confiscated from former supporters of Parliament. 19th century Sandgate Castle was still in use during the Napoleonic Wars at the start of the 19th century, but was heavily rebuilt. Brigadier-General William Twiss surveyed the south coast in 1804, and proposed building a series of 58 new defensive towers along it, as part of which he proposed converted Sandgate into a "secure sea battery". After some opposition, and many delays within the War Office, the work on the castle finally began in 1805. The project lowered the height of the castle considerably, destroying much of the fortification in the process. The