To protect London and other Thames settlements during World War II, the Royal Navy built several Maunsell forts , named after their designer, Guy Maunsell . During the war, the forts shot down 22 aircraft and about 30 flying bombs. They were decommissioned in the late 1950s. During the 60s, many of them were used as offshore pirate radio stations , as their size made them ideal antenna platforms. Today, Fort Roughs is occupied by a family claiming that the fort is an independent nation, called the Principality of Sealand