Upnor Castle was constructed between 1559-67 to defend the Chatham Dockyard and Reach which was at the time the primary port for the British Navy. In June 1667, the Dutch launched a surprise raid on Chatham. The entered the reach and burned and captured a number of ships. The defensive positions such as Upnor were severely hampered by a lack of ordinance supplies and thus were unable to prevent the progress of the Dutch fleet up the river. They were resupplied overnight and when the Dutch returned the next day intent on burning the dockyard, Upnor and the other positions were successful in driving them off before they reached their target. However, the raid had shown that any raid needed to be stopped before it got that close to the dockyard and so a series of larger forts were built nearer the Thames. Upnor became a gunpowder and cannon store for ships visiting the Dockyard. It remained a military establishment until 1945 when it passed to the Dept of Monuments and is now open to the Public and managed by English Heritage.