The Fort can be visited
Coalhouse Fort

Coalhouse Fort, a fortress in England, is situated on the banks of the River Thames near Tilbury. It was built as part of coastal defense and played a role in protecting London.
History+
The origins of Coalhouse Fort date back to an earlier artillery battery. In the 1860s, at the suggestion of the Royal Commission on the Defence of the United Kingdom, a reconstruction took place, completed in 1874. During World War II, the fortress served as a site for equipment to monitor the magnetic fields of ships, countering the threat of naval mines.
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This description draws on the facts documented in the linked Wikipedia article; Wikipedia content is licensed under CC BY-SA 4.0. Wording and editing: Mobile History.
Location: 51.4649, 0.4329