The Royal Commission of 1859 identified the need to strongly defend the approaches to the Royal Dockyard at Chatham via the Medway.  Hoo Fort was part of this defence strategy and was one of two circular forts (the other being Fort Darnet) that was built in the Medway itself.  It was a very difficult build, beset with continual construction problems such as repeated subsidence because of the unstable ground on which the fort was built.

Hoo Fort is a two-tiered building with the gun casemates on the upper level and below them was the barrack accommodation and magazines. The lower level is wider than the top, and access was gained via a drawbridge and short tunnel into the lower level.  

A central pillar within the fort has steps around its circumference leading to the upper level. Inside the central pillar were a water tank, toilets and ablutions.  Bridges extend out from the top of this central pillar to the gun casemates.  The guns themselves were protected by iron shields, which were originally painted in lines in an attempt to make them blend with the surrounding stonework of the fort.  Fireplaces within the casemates would have allowed for them to be used as barrack accommodation, should the necessity have arisen.

On the lower level, where the magazines are located, the fort is separated into three concentric rings, each one having a very different and defined purpose.  The inner ring was the lighting passage, along which access to all the lamp recesses on this level could be gained.  The central ring was the ammunition passage, containing the bottom of the ammunition lifts (shell and cartridge hoists).  The outer ring consisted of the shell and cartridge stores.

When it was built, Hoo Fort was a state of the art fortification; it was armed with 11 x 9” RMLs, which stayed there until the end of the nineteenth century.  It saw use as an observation post during the First World War and during the Second World War a minewatching post was built on its roof.  After the war ended, Hoo Fort was abandoned.