Upnor Castle

The upper Medway was a fine berth for warships: sheltered by hills, slow-flowing and free of rocks. Under Henry VIII it became the principal anchorage for royal ships lying "in ordinary", and the storehouses at Gillingham and Chatham grew into Chatham Dockyard. Yet the river had no defences; Rochester and Queenborough castles both faced the landward approaches.

Elizabeth I and her Privy Council commissioned a fort in 1559. Six "indifferent persons" chose a site opposite St Mary's Creek, six acres taken by the Crown from Thomas Devinisshe of Frindsbury for £25. The design was Sir Richard Lee's, though he was absorbed in the defences of Berwick-upon-Tweed; his deputy Humphrey Locke oversaw the work and Richard Watts, a former mayor of Rochester, kept the accounts. The main block stood by 1564, but three more years and extra funds were needed to finish it, at a total cost of £4,349.

The undeclared Anglo-Spanish War of 1585–1604 found the castle poorly manned until the Lord High Admiral, Charles Howard, 1st Earl of Nottingham, pressed for a larger garrison; by 1596 eighty men held it at eight pence a day. A chain was stretched across the river below the castle, and between 1599 and 1601 Sir John Leveson had the defences strengthened with a new ditch, a palisade before the Water Bastion and a landward gatehouse and drawbridge. A survey of 1603 counted twenty guns in the castle and eleven more in the Bay and Warham Sconces, with thirty-four longbows still on the garrison's books.

In 1642 Upnor fell to Parliament without a fight and was used to intern Royalist officers. The Royalist rising of May 1648 seized Gravesend, Rochester, Dover and Maidstone, but the Royalists were beaten at the Battle of Maidstone on 1 June and the castle returned to Parliament. Sir Thomas Fairfax inspected it and ordered the gun platforms strengthened; the towers were built up, and in 1653 their open backs were closed to make them fit for troops.

The castle saw action once. In June 1667, during the Second Anglo-Dutch War, a Dutch fleet under the nominal command of Lieutenant-Admiral Michiel de Ruyter captured Sheerness, sailed up the Thames to Gravesend and then up the Medway, passed the chain meant to bar the river, and towed away HMS Royal Charles and HMS Unity while burning other ships at anchor. The Dutch lay in the river overnight on 12 June while the Duke of Albemarle ordered an eight-gun battery thrown up beside the castle. When they attempted a second time to pass Upnor for Chatham, the castle's guns, the garrison's muskets and the new battery bombarded them; they burned more ships but could make no further progress and had to withdraw. The outcome has been described as "the worst naval defeat England has ever sustained".

The pro-government London Gazette reported that the Dutch were "so warmly entertained by Major Scot, who commanded there", and by Sir Edward Spragg's battery on the shore, that they were forced to retire — of which the military historian Norman Longmate observes tartly that "in presenting damning facts in the most favourable light Charles [II's] ministers were unsurpassed". Samuel Pepys came closer to the truth: the garrison "shot till they had hardly a gun left upon the carriages, so badly provided they were".

The raid ended Upnor's career as a fortress. Stronger forts were built farther down the Medway and on the Isle of Grain, and in 1668 Upnor was converted into "a Place of Stores and Magazines", supplying munitions to warships lying in the Medway or the Swale. By 1691 it was England's leading magazine, holding 164 iron guns, 7,125 pieces of iron shot and 5,206 barrels of powder — considerably more than the next largest magazine, the Tower of London.

A new magazine downstream in 1811 relieved the pressure; after 1827 it ceased to serve as a magazine and became an Ordnance Laboratory for filling shells. After the First World War the site became a Royal Naval Armaments Depot, and from the 1920s the castle was increasingly a museum — though still part of the Magazine Establishment when two enemy bombs fell in 1941, dislodging plaster that had hidden old graffiti, among it a drawing of a ship of about 1700.

With the war over in 1945 the Admiralty approved the castle's use as a departmental museum and its opening to the public, and restoration followed. It was scheduled as an ancient monument in January 1960 and listed Grade I in 1986. Upnor Castle is managed today by English Heritage and remains part of the Crown Estate.