The Fort itself was built as a Victorian Coastal Defence in 1874, and its primary purpose was to defend London from any invasions from neighbouring countries such as France. It has a maze of tunnels and rooms projecting from every dimension and plenty of areas for investigation. Along with over 600 years of military history, it also has a gruesome past.

Coalhouse Fort is a former artillery fort built in the 1860s to guard the lower Thames against seaborne attack. It stands at Coalhouse Point in Essex on the north bank of the river, at a location that was vulnerable to raiders and invaders. It was the last in a series of fortifications dating back to the 15th century and was the direct successor to a smaller mid-19th century fort built on the same site. Constructed during a period of tension with France, its location on the marshy ground caused problems and led to a lengthy construction process.

The fort was equipped with various large-calibre artillery guns and the most modern defensive facilities at the time, including shell-proof casemates protected by granite facing and cast-iron shields. However, its slow construction and the rapid pace of artillery development meant that it was virtually obsolete for its original purpose within a few years of its completion.

The fort\'s armament was revised several times during its seventy years of military usage as its role in the river\'s defensive system evolved. It was initially a front-line fortification supported by Shornemead Fort and Cliffe Fort located south and east on the Kent shore. Over time, as batteries and forts further downriver became the front line of the Thames defences, Coalhouse Fort was stripped of its primary weapons. Its fabric was altered to support smaller quick-firing guns intended against the fast-moving surface and aerial targets. Its last military usage was as a training facility for a few years after World War.

Decommissioned in 1949, the fort was used for a time as a storehouse for a shoe company before the local council purchased it. Despite its historical and architectural significance, the surrounding land was developed into a public park, but the fort fell into dereliction. Since 1985 it has been leased to a voluntary preservation group working to restore the defence and use it for various heritage and educational purposes. The public can visit it on regular open days, and it houses several reconstructions, small military museums and open-air displays of military equipment.