X-Pilot: A Trip to Redsand Fort

The Maunsell Forts are towers built in the Thames and Mersey estuaries during the Second World War to help defend the United Kingdom. They were operated as army and navy forts, and named for their designer, Guy Maunsell. The forts were decommissioned during the late 1950s and later used for other activities including pirate radio broadcasting. (from wikipedia)