Sandsfoot Castle, also known historically as Weymouth Castle, is an artillery fort constructed by Henry VIII near Weymouth, Dorset. It formed part of the King's Device programme to protect against invasion from France and the Holy Roman Empire, and defended the Weymouth Bay anchorage. The stone castle had an octagonal gun platform, linked to a residential blockhouse, and was completed by 1542 at a cost of £3,887. Earthwork defences were built around the landward side of the castle, probably in 1623. Sandsfoot saw service during the English Civil War, when it was held by Parliament and Royalists in turn during the conflict. It survived the interregnum but, following Charles II's restoration to the throne, the fortress was withdrawn from military use in 1665.
Portland Castle is an artillery fort constructed by Henry VIII on the Isle of Portland, Dorset, between 1539 and 1541. It formed part of the King's Device programme to protect against invasion from France and the Holy Roman Empire, and defended the Portland Roads anchorage. The fan-shaped castle was built from Portland stone, with a curved central tower and a gun battery, flanked by two angular wings. Shortly after its construction it was armed with eleven artillery pieces, intended for use against enemy shipping, operating in partnership with its sister castle of Sandsfoot on the other side of the anchorage. During the English Civil War, Portland was taken by the Royalist supporters of King Charles I, and then survived two sieges before finally surrendering to Parliament in 1646.