The Maunsell Forts of the Thames Estuary
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.
As a result of German mining activity at the outbreak of war in September 1939, an urgent need arose to protect the waters of the Thames Estuary from small naval craft aircraft sowing magnetic mines. The initial answer was the placing of four Naval Sea Forts, each armed with two 3.7” Heavy AA guns and two 40mm Bofors guns, in the Estuary, located as follows: one 7 miles off Harwich, Essex, one 7 miles off Frinton on Sea, Essex, one 5 miles off Margate, Kent and one 12 miles off Herne Bay, Kent. Each of these Forts was manned by 120 men and three officers with crews rotating every six weeks to shore bases at Harwich for the Essex forts and Sheerness for the Kent Forts.
These four Naval Forts were placed in the Thames Estuary between February and August 1942 and served throughout the war until abandoned in 1956. Of the four Forts, only two now exist, Roughs Tower off Harwich, now known as the Principality of Sealand and occupied by “Prince” Roy Bates and his family and Knock John, abandoned and unoccupied off Shoeburyness. Sunk Head Fort off Frinton on Sea was blown up on Government instructions in the 1960’s to stop the Radio Pirate activity and Tongue Sands off Margate collapsed into the sea during a storm in 1966.
As a result of German activity it was decided to build another type of Fort to deter German aircraft from using the River Thames as a navigational aid to find the centre of London and the hugely important Dockland area of that period. Guy Maunsell was again asked to design a suitable structure to meet this need. This time he came up with a totally different answer in the shape of seven towers joined together by catwalks. The seven towers consisted of a Bofors Tower with two 40mm Bofors guns, four towers with 3.7” HHA guns, a Contol Tower housing predictors and radar and a Searchlight Tower.
The towers were built at the Red Lion Wharf site in Gravesend, towed down river and lowered by hand winch onto the sea bed, each tower taking up to eight hours to be placed in position. The first set of towers were placed at the Nore between May and July 1943, the second set, the Redsand Fort between July and September 1943. The final set, the Shivering Sand Fort between September and December 1943. Crewed initially by 165 men, this figure was increased to 265 after June 1944 when the German Luftwafe started to use the V1 Flying Bomb (Doodlebug). These new weapons were much faster than aircraft of that period and it was necessary to have men at their gun positions to have a chance of hitting them.
The period on board for the crew was four weeks followed by a ten day break ashore at the Drill Hall, Gillingham, Kent. The unit was known as the First A.A. Fort Regiment R.A. (Thames) which was disbanded at the end of the war and replaced by the “Fort Maintenance Detachment R.A”. In wartime, supplies were ferried out to the Forts by the R.A.S.C. Water Transport Company from Sheerness in Kent using small armed trawlers. During the wartime period all the Forts in the Thames Estuary were responsible for shooting down 21 aircraft and 30 plus “Doodlebugs”.
The maintenance crews were in occupation from May 1945 until April 1956 when it was decided to remove the guns and abandon the Forts. On March 1st 1953 a ship, the “Baalbeck” ran into the Nore group of towers in thick fog and knocked over the Bofors Tower and a gun tower killing four of the installed maintenance crew. The Army seemed more concerned with the loss of equipment, two Bofors guns, a 3.7” gun and a large amount of equipment and stores, then the personnel whose relatives were paid paltry sums as compensation for the loss of their loved ones. Subsequently in 1959 the Nore group of towers were removed and scrapped.
Another accident happened in 1963 when in June a ship the “Riberborg” crashed into the Shivering Sand Fort and demolished a gun tower. Fortunately, no one was on board at the time and there were no casualties. Thus, Shivering Sand Fort today consists of only six towers.
This left the Redsands and Shivering Sand Forts remaining out of the three sets and following a period of occupation by the Radio Pirates from 1964 to 1967 the Forts were sanitized by the Admiralty who removed access ladders and catwalks to deny people access.
Today, Redsand Fort as the only complete structure as built in wartime is the focus of attention by Project Redsand, a group of enthusiasts with the aim of reinstating the Fort to its original built condition. Having had an underwater survey carried out by the Port of London Authority at a cost of around £5,000, work has progressed to installing a new access system to the G1 tower thanks to the generosity of Mowlem Marine (now Carillion) of Northfleet. Built at a cost of approximately £40,000, the access system enables project members to board the tower to commence restoration.
A new survey of the above water structures is being conducted by Taylor Woodrow and once this is complete, a museum and other installations will enable the Fort to take its place as a monument to the ingenuity of Guy Maunsell who used the Army Fort design to pave the way for oil and gas exploration rigs in the North Sea in the 1950’s.
NB. Military equipment installed on the Forts consisted of 3.7” guns Mk 2c with automatic loaders by Mollins of Deptford. Radar No 3 Mk 2 subsequently updated and modernised to Radar No 3 Mk 7. Sperry Predictors No 11 and Searchlight No 2 Mk 2.
Copyright Frank R Turner, 2006.