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. One of the forts is managed by the unrecognised Principality of Sealand; boats visit the remaining forts occasionally, and a consortium called Project Redsands is planning to conserve the fort situated at Red Sands. In the summers of 2007 and 2008 Red Sands Radio, a station commemorating the pirate radio stations of the 1960s, operated from the Red Sands fort on 28-day Restricted Service Licences. The fort was subsequently declared unsafe, and Red Sands Radio has moved its operations ashore to Whitstable.
Maunsell also designed forts for anti-aircraft defence. These were larger installations comprising seven interconnected steel platforms. Four towers carried QF 3.75 inch guns arranged in a semicircle ahead of the control centre and accommodation, a tower to the rear of the control centre mounted Bofors 40 mm guns, while the seventh tower, set to one side of the gun towers and further out, was the searchlight tower.
Each of these AA forts carried four QF 3.75 inch guns and two Bofors 40 mm guns. During World War II, the Thames estuary forts shot down 22 aircraft and about 30 flying bombs. They were decommissioned by the Ministry of Defence in the late 1950s.
There are 7 forts in the Red Sands group, at the mouth of the Thames Estuary. These forts were previously connected by metal grate walk-ways.
Various forts were re-occupied for pirate radio in the mid-1960s.
In 1964, a few months after Radio Caroline went on air, Screaming Lord Sutch set up Radio Sutch in one of the towers at Shivering Sands. Sutch soon became bored with the project and sold the station to his manager Reginald Calvert who renamed the station Radio City and expanded operations into all of the five towers that remained connected. Calvert's killing in a dispute over the station's ownership (found to be self-defence rather than murder) contributed to the Government passing legislation against the pirates in 1967.
During the pirate era the Port of London Authority frequently complained that its monitoring radio link was being disrupted by the nearby Radio City transmitter.
Red Sands was likewise occupied by Radio Invicta, which was renamed KING Radio and then Radio 390, after its wavelength of approximately 390 metres. The station's managing director was ex-spy and thriller writer Ted Allbeury. The 1965 Danger Man episode "Not-so-Jolly Roger" was partly filmed at Red Sands and includes an acknowledgement to Radio 390 in its closing credits. Red Sands was also used for the 1968 Doctor Who serial Fury from the Deep, in which the complex stood in for a North Sea gas refinery besieged by an intelligent seaweed creature.
The size of the Army forts made them ideal antenna platforms, since a large antenna could be based on the central tower and guyed from the surrounding towers.
A small group of radio enthusiasts set up Radio Tower on Sunk Head Naval fort, but the station was run on a shoestring, had poor coverage and lasted only a few months. Claims by the group that they also intended to run a television service from the fort were never credible. In order to prevent further pirate broadcasting, a team of Royal Engineers laid 2,200 lbs of explosive charges on Sunk Head, commencing on 18 August 1967. At 4:18 PM on 21 August the charges were detonated, destroying the entire superstructure and most of the concrete legs above the waterline.
Paddy Roy Bates occupied the Rough Sands Fort and set up Radio Essex, later renamed BBMS—Britain's Better Music Station—but was better known for his post-pirate activities. He, or a representative, has lived in Roughs Tower since 1964, self-styling the tower as the Principality of Sealand.