Anyone who is familiar with London knows that the river Thames flows through it and empties out into the English Channel. In the early years of the second World War, the British government had army sea forts built in the Thames Estruary to provide anti-aircraft fire in the area. Designed and built by Guy Maunsell, for who they are named, the sea forts are a collection of 7 towers with walkways connecting each to the central control tower. The towers were fitted with two 3.75-inch guns and two 40 mm Bofors guns.
In the 7 tower arrangement, the control tower was at the centre of the grouping, with the towers fitted with guns in a protective semi-circle around the control tower, with a search light tower in the back of the grouping. In all, there were four forts built and their job was to deter and report German air raids or any attempts to lay mines in the waters of the Channel. The forts exceeded expectations, shooting down 22 planes and 30 flying bombs. In the years immediately following the war, the British government wanted more built, but none of the plans moved forward.
In the mid-1960s, some of the towers were used by groups for pirate radio stations. In 1964, Radio Sutch (later renamed Radio City) began broadcasting from one of the towers in Shivering Sands Fort. Various other radio stations set up shop in other forts because the size of the towers allowed for a wider broadcast area. Paddy Roy Bates set up Radio Essex in Rough Sands Fort. Either he or a representative of his has lived in the fort since 1964 after creating the micronation of the Principality of Sealand.
Whatever is left of these forts today, they stand as sentries to a by-gone era.
Wikipedia and Underground Kent