This Tudor Artillery fortress wasbuilt in 1559 to protect the royal dockyard of Chattam and fleet anchoragein the River Medway.

It was Queen Elizabeth I who orderedto built this gun fort.

After the defeat of the Spanish Armada in 1588 there was still fear of attack and inn 1599 the fort was strenghtened and looked much likewe see it today.

Thecastle saw active service in 1667 when the Dutch sailed up the River Medway to attack the British fleet at anchor. The Dutch inflicted a terrible humiliationtowing away the Royal Charles.

In 1668 Upnor was downgraded to be used as a magazine, supplying powder and shot to warships anchored in the river.