Coordinates: 51°24′24″N 00°35′49″E / 51.40667°N 0.59694°E / 51.40667; 0.59694
Fort Darnet, like Fort Hoo was built on the recommendations of the 1859 Royal Commission on an island covering the inner navigable channel of the River Medway, Kent.
Originally designed for two tiers of guns mounted in a circle, with a boom strung between them, there were many problems with subsidence, and after extensive cost overruns the forts were completed in 1871 with one tier, and 11 guns : a mixture of 9-inch and 7-inch rifled muzzle-loaders, and no boom. The forts were never used in anger, and were disarmed before the First World War.
In the Second World War the fort was used as observation posts, with platforms and pillboxes built on top. The fort is still in fair condition, however the magazine level seems to have been deliberately flooded to minimise access and vandalism. The island can be freely visited by boat, though the landing is muddy.