The Maunsell Forts are armed 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 after their designer, Guy Maunsell. The forts were decommissioned in the late 1950s and later used for other activities including pirate radio broadcasting. Sealand was founded as a sovereign Principality in 1967 in international waters, seven miles off the eastern shores of Britain.