Sandgate Castle is an artillery fort originally constructed by Henry VIII in Sandgate in Kent, between 1539 and 1540. It formed part of the King's Device programme to protect England against invasion from France and the Holy Roman Empire, and defended a vulnerable point along the coast. It comprised a central stone keep, with three towers and a gatehouse. It could hold four tiers of artillery, and was fitted with a total of 142 firing points for cannon and handguns.

The Device Forts, also known as Henrician castles and blockhouses, were a series of artillery fortifications built to defend the coast of England and Wales by Henry VIII. Traditionally, the Crown had left coastal defences in the hands of local lords and communities but the threat of French and Spanish invasion led the King to issue an order, called a "device", for a major programme of work between 1539 and 1547. The fortifications ranged from large stone castles positioned to protect the Downs anchorage in Kent, to small blockhouses overlooking the entrance to Milford Haven in Pembrokeshire, and earthwork bulwarks along the Essex coast. Some forts operated independently, others were designed to be mutually reinforcing. The Device programme was hugely expensive, costing a total of £376,000 ; much of this was raised from the proceeds of the Dissolution of the Monasteries a few years before.