 New and stronger forts were built further downriver over the following two centuries, culminating in the construction of massive casemated forts such as Garrison Point Fort, Hoo, and Darnet Forts.Upnor Castle became a naval ammunition depot, storing great quantities of gunpowder, ammunition, and cannon to replenish the warships that came to Chatham for repair and resupply.It remained in military use until as late as 1945.