At the outbreak of World War II, the Port of London was the busiest port in the world. As such, a large proportion of supplies to the UK entered by ships navigating the Thames. The German Navy quickly sought to put a stranglehold on this route, and to this end, utilised a new secret weapon – the magnetic influence mine. Whilst there were different variants of this mine, in simplistic terms, the mine was detonated by the presence of a large magnetic object – such as a steel hulled ship – passing in close proximity, without having to make physical contact.
So successful was this that in the first few months of the war, over one hundred ships were sunk in the Thames Estuary alone. It was clear that urgent action was needed to stem these losses, and as most mines were laid by aircraft, ships were requisitioned and used as mobile anti aircraft units. However, this was not altogether successful, and a more satisfactory solution was needed.In the early years of the war, Guy Maunsell, a civil engineer, had produced plans for offshore defences.
At the time his ideas were considered somewhat eccentric, but he was asked to submit plans for an offshore fort as an effective means of dealing with the laying of the mines. Plans were drawn up, and after some modification, approval was given for the manufacture and installation of four offshore forts. These were of mainly reinforced concrete construction, built on land on a lozenge shaped reinforced base, and towed out to sea where they were sunk onto the seabed.
Each fort accommodated approximately 120 men, housed mainly within seven floors of the 24’ diameter twin reinforced concrete legs. These forts were under the control of the Navy, and were individually known as HM Fort Roughs Tower, Sunk Head Tower, Tongue Sands, and Knock John. They were all placed in position between six and twelve miles offshore between February and June, 1942. They became operational immediately.In early 1941, Maunsell was contacted by the Admiralty to design defences in the Liverpool bay area of the Mersey. Seabed conditions dictated a different form of construction.
Each tower was built off a reinforced concrete base of ‘Oxford picture frame’ design. Four hollow reinforced concrete legs of 3’ diameter supported the 36’ x 36’ steel house of two floors, with the military equipment installed on the top deck. Each fort comprised seven towers linked by tubular steel catwalks. In addition to the Mersey forts, three forts of similar construction were built in the Thames estuary, between May and December, 1943. They were known as the Nore, Redsand and Shivering sands Army Forts.
Each fort accommodated up to 265 men.Both Army and Navy forts successfully acquitted themselves during the war years. Whilst the Mersey forts never fired a shot in anger, the Thames forts shot down 22 planes, 30 flying bombs, and were instrumental in the loss of one U-boat, which was scuttled after coming under fire from Tongue sands tower.After the war the forts were placed on ‘care and maintenance’. However as the need for their continued use diminished, they were abandoned, and the guns removed from the Army forts, in 1956.The Nore fort was dismantled in 1959 being considered a hazard to shipping [two towers were lost following a collision in 1953] whilst one of the Shivering Sands towers was similarly lost in 1963.In 1964, Radio Caroline began broadcasting from a ship moored outside UK Territorial Waters.
Other broadcasters followed with pop star Screaming Lord Sutch establishing Radio Sutch on the Shivering Sand Towers – much to the embarrassment of the Government. Radio Sutch became Radio City, whilst other forts were occupied to become Radio 390 [Redsand], Radio Essex [Knock John], and Tower Radio [Sunk Head]. The forts fell silent after a number of prosecutions in late 1966/67. It was accepted that all were within territorial waters, other than Roughs and Sunk Head. Sunk Head was destroyed by the Royal Engineers shortly after the Marine Broadcasting Offences Act became law, although Roughs has been occupied since 1967 to this day as the quasi independent Principality of Sealand.
Tongue Fort collapsed following a severe storm in 1996, although had been abandoned as long ago as 1947, after the reinforced pontoon base broke its back, and one of the legs developed a list.The remaining Army forts had their catwalks removed for safety reasons, and apart from some usage by the SAS as simulated oil rig assault training, all have remained largely unchanged, and are viewed from the coast as a curiosity on the horizon, by the casual observer.
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