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Awesome Thames Forts - Built to protect London from air raids.

Updated on September 28, 2016
Maunsell Navy Fort being towed into place
Maunsell Navy Fort being towed into place
Tricky moment as pontoons are flooded
Tricky moment as pontoons are flooded
Maunsell Navy Fort in position and ready for action
Maunsell Navy Fort in position and ready for action
Cross section of a Maunsell Navy Fort
Cross section of a Maunsell Navy Fort
Maunsell Army Fort building in dry dock at Gravesend
Maunsell Army Fort building in dry dock at Gravesend
Maunsell Army Fort being towed into position
Maunsell Army Fort being towed into position
Maunsell Army Fort view 1944
Maunsell Army Fort view 1944
Maunsell Army Fort before decommissioning
Maunsell Army Fort before decommissioning
Maunsell Army Fort
Maunsell Army Fort
Maunsell Army Fort
Maunsell Army Fort
Maunsell Army Fort - Shivering Sands
Maunsell Army Fort - Shivering Sands
Current interior shot of Maunsell Army Fort
Current interior shot of Maunsell Army Fort
Current interior shot of Maunsell Army Fort
Current interior shot of Maunsell Army Fort
Maunsell Army Fort
Maunsell Army Fort
Map of positions of both Navy and Army Forts
Map of positions of both Navy and Army Forts
In operation with the walkways in place
In operation with the walkways in place
Diagram of the make up of each of the army forts
Diagram of the make up of each of the army forts
During the war years
During the war years
Army forts being built at Gravesend
Army forts being built at Gravesend
Bofors anti aircraft guns mounted on various forts
Bofors anti aircraft guns mounted on various forts

Thames Forts

Those of us who were brought up in this area of Kent became used to seeing these ghostly monsters standing with the sea mist swirling around their long legs looking for all the world like some ghastly alien machine. They came into existence in 1941 when Britain stood alone in the world against the ruthless Nazi war machine. When the Luftwaffe failed to break the RAF, during The Battle of Britain, they switched their saturation bombing techniques from airfields to softer civilian targets, such as cities, towns, factories and dockyards.

German aircrews needed little in the way of navigational skills, all they needed to do was find the Thames estuary and follow the river right into the heart of London. In the early days of the war the route along the estuary was poorly defended and the massed hordes of enemy aircraft, apart from being constantly harried and torn apart by Hurricanes and Spitfires, had little to fear from ground defences.

At the start of the bombing offensive on London this undefended area became quickly obvious and it was decided to provide some off-shore defence platforms which would be permanently manned and provide anti-ship artillery and anti-aircraft support.

These off-shore defence platforms were to be called the “Thames Estuary Special Defence Units” and from the various designs those by Guy Maunsell were chosen and henceforth they were known as the “Maunsell Forts”. Two very different units were to be built, one classified as Naval Sea Forts and the other as Army Sea Forts.

Naval Sea Forts

Work was started shortly after July 1941 and there were to be 5 forts built. In the event only 4 were actually constructed and they were named after their estuarial position. In order of build they were:

HMF Roughs Tower U1– in position 11th Feb 1942. This fort was in action against enemy aircraft just 30 minutes after being positioned. Following decommissioning at the end of the war it stood abandoned until the start of the various boarding’s by pirate radio stations. After a series of violent confrontations with a rival station owned by Ronan O'Rahilly it was finally occupied in 1967 by a Southend businessman by the name of Major Paddy Roy Bates. All of the guns and military equipment were literally tipped over the side. Mr Bates proclaimed it a principality and renamed it “Principality of Sealand” adopting the title of Crowned Prince Roy. In addition to its own currency he has his own postage stamps printed but they are not recognised by the Postal Union. Roy died on 9th Oct 2012 and his son Prince Regent Michael now becomes head of the principality.

HMF Sunk Head Tower U2 – in position 1st June 1942 (Destroyed deliberately by the military 21st Aug 1967 using 3200lb PE4 plastic explosive to stop its use as a pirate radio station) Twenty feet of the legs remained which were struck by a liquid gas carrier.

HMF Tongue Sands U3 – in position 27th June 1942 (Destroyed by a storm 21st Feb 1996) Credited with the destruction of E-Boat S-199 with shelling from its 3.7 inch guns. Eventually broke its back, guns were removed by Chinook helicopter from RAF Manston and the structure collapsed into the sea leaving just 18ft of the south leg. One of the 3.7 inch guns is on display at New Tavern Fort – Gravesend.

HMF Knock John U4 – in position 1st Aug 1942. In major action against enemy aircraft on 3rd March 1943, 12th April 1943 and 3rd February 1944 and many, many other minor engagements. On 12th May 1944 a USAAF B-17G-15-BO Flying Fortress named "Lady Stardust ll" (Serial no. 42-31345 from 452 Bomb Group) crashed around 1 mile west of the Fort. It had taken part in a raid on a Czechoslovakian oil refinery in Bruz but was severely damaged and had only one engine operating. It was piloted by 2nd Lt Milan Marecek, F/O Harold Eastman as co-pilot, 2nd Lt Lawrence P. Defeo as navigator, 2nd Lt Cornelius Kohlman as bombardier, Staff Sgt Merle D. Orcutt as engineer, Staff Sgt Dwight N. Miller as radioman, Sgt Sam N. Fain as BT-Gunner, Sgt Ernest M. Hughinson as RW-gunner, Sgt Donald F. Kemmann as LW-gunner and Sgt George Bouchek as T-gunner. The engineer, Merle Orcutt, had been wounded in the head by 20mm round from an attacking German fighter and died instantly. When the plane ditched, his body could not be recovered before the plane sank. Alerted by the fort all remaining 9 members of the crew were picked up by Air Sea Rescue.

In June 1992 Knock John forts guns were removed by RAF helicopter.

The navy forts were quite basic in design and were primarily intended to protect shipping against e-Boat raids, submarines and mine dropping bombers. Two 24ft dia. hollow re-enforced pillars were constructed each containing several rooms for the accommodation of 120 men (90 Marines & 30 Sailors) & 3 officers. Spread across the two pillars was a platform about 110ft x 35ft where the guns were installed. The entire structure was mounted on a hollow 14' deep pontoon, at 4500 tons these monsters measured 110' from the sea-bed to the top of the radar house, deck level was 75' above the sea-bed The armament comprised two Vickers-Armstrong 3.7" static MK2c Heavy Anti-Aircraft Guns at each end with a fire rate of 10-20 rounds per minute and two light 40mm Bofors Anti-Aircraft Guns with a fire rate of 120 rounds per minute the combined force of which would give them quite a sting. They also were equipped with 4 light Lewis machine guns for low flying raiders, although these were later removed and replaced with twin Browning machine guns. On the gun platform a small upper deck was built with a radar platform on top of that. A 27ft motor boat was slung underneath the wings.

The pontoons allowed these impressive structures to be built in dry-dock by Holloway Brothers (London) Ltd using semi-skilled labour at Red Lion Wharf - Gravesend and they were constructed, fitted out & commissioning in just 53 days. They were towed out & grounded in around 40ft of water with a tidal rise and fall of approximately 20ft. Although all the calculations had shown these designs were strong there was considerable tension when the sea cocks were opened and water flooded the pontoon. The structures were inherently top heavy and many feared that they would simply tip over and "turn turtle" during final placement. To everyone’s relief this was not the case and fifteen minutes after opening the seacocks the pontoon submerged. Twenty seconds later the leading edge of the pontoon hit the sea bed with the large reinforced concrete "buffer", which was designed to crush when it hit the bottom, dissipating some of the force which could have damaged the pontoon itself. Ninety seconds later the pontoon became completely filled with sea water, and the whole structure became fixed firmly to the seabed.

The Naval Fort design was the basis for the Mulberry Harbours. Sinking large reinforced concrete structures onto an unprepared seabed hadn't been tried before. Examples of the Mulberry Harbour can be seen in Portland Harbour in Dorset

Army Sea Forts

As mentioned these were also designed by Guy Maunsell and their primary use was to provide anti-aircraft fire against bombers and raiders using the Thames estuary approach to London and the Kent and Essex area.

Each fort comprised 7 towers with tubular steel walkways connecting each to a central control tower. Apart from the control tower there was one Bofors tower, four later mk6 3.7 inch gun towers, with a fire rate of 30 rounds per minute and one searchlight tower. A clinker built motor lifeboat fully provisioned was slung under the control tower. Army Crews spent a month at sea then two weeks ashore. Conditions for the crew were comfortable with plenty of light, oil fired central heating, daily hot salt water baths & excellent food prepared in the Control Tower Cook House.

In order of building they were:

HMF Nore Army Fort U5 (No longer standing – dismantled in 1959) (Damaged in a storm 1953 and two months later on the 1st March the Bofors and one gun tower were destroyed in a collision with a Swedish pulp carrier the 'Baalbek' that killed 4 caretakers. In late 1954 there was another collision when the 'Mairoula' crashed into the Great Nore Fort damaging a Towers reinforced concrete leg which was repaired.

HMF Red Sands Army Fort U6 (Used as a pirate radio station in 1960/70s) Now abandoned but still standing. Possible demolition planned but a preservation society started as fort is in good condition. This is the only fort still standing in original wartime condition. Over the years various television programmes and films have been made using this fort, but this ceased when the military pulled down all of the connecting walkways using grappling irons. At the same time the SAS used them for oil rig assault training.

HMF Shivering Sands Army Fort U7 Towards the end of the war this fort had its searchlight removed and uprated radar equipment installed. Following the Great Flood of 3rd February 1953, the Port of London Authority (PLA) took over the isolated Searchlight Tower and in the early 1960s installing automated wind & tide gauges. A while after the Shivering Sands Fort was used for radar prediction & special paint trials, perhaps explaining its good external finish. (It was used as a pirate radio station in 1960/70s) (Only 6 towers remaining as one hit and destroyed by MV “Ribersborg” in heavy fog in 1963.) Now abandoned but still standing.

Building of the 21 towers started in Aug 1942 and they were all in position and fully operational by Dec 1943. In each case the Bofors tower was positioned first so that it could defend the tugs and construction teams assembling the remaining six towers.

Like the naval forts these were all quickly constructed in dry dock at Gravesend by the same company that built the previous Forts and were floated out to sea, hauled by tugs and grounded in water no more than 100ft deep. Access to the forts was via fixed ladders to an entrance at the base of the platform.

All three of the forts were operational immediately they were finally positioned and all saw significant action throughout the war. The Naval and Army Forts between them are accredited with shooting down 22 enemy aircraft and 31 "Doodle Bug" V1 flying bombs. In addition Tongue Sands Naval Fort sank a German E-Boat (reported to be S-199 of the 8 Schnelboot Flottilla) operating out of Ijmuilden Holland.

Following the end of the war, on the 14th June 1945 the Forts were officially decommissioned & placed on “care & maintenance”. Servicing was carried out by the Motor Fishing Vessel MFV 1037 of Harwich attached to HMS Wildfire. The crews aided by civilians spent 4 weeks aboard before being relieved & spending between 7-14 days ashore. In 1952 all Army Forts were re-equipped with new search lights and up-rated radar equipment. But in 1956 the Army decided they had no further use and using a large floating crane from Chatham Dockyard removed all guns and equipment. Trinity House looked briefly at the Naval Towers as Lighthouses but this came to nothing. In 1956 the Ministry decided the Forts were of no further use, but they were looked after for another two years with caretaker crews. Eventually in 1958 they were abandoned to their own fate and the elements

During the mid-1960s all of the Naval Forts (except HMF Knock John which is inside the 3 mile limit) were boarded and used as pirate radio stations. HMF Sunk Head Tower was taken over by a pirate broadcaster called Radio Essex who planned to transmit television pictures after the BBC closed each day. Unfortunately they ran out of money before it could come to fruition.

WW2 Thames defence forts

Have you seen or heard of these specialist forts built to protect London ?

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© 2012 Peter Geekie

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    • Peter Geekie profile image
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      Peter Geekie 13 months ago from Sittingbourne

      Dear Hector,

      Yes most still exist, although they are quite rusty. The only one in good condition is Sealand. They run high speed RIB trips out to the forts.

      kind regards Peter

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      Hector 13 months ago

      Fascinating hub do these monsters still stand?

    • Peter Geekie profile image
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      Peter Geekie 4 years ago from Sittingbourne

      Dear krillco,

      Thank you very much for your kind comments. You're quite right they presented a tempting target and were attacked on a regular basis. However two 3.7 inch anti-aircraft guns and a rapid fire Bofors set-up with experienced and accurate gunners soon took the fun out of getting any closer than a few miles from them. High altitude bombing was a possibility but don't forget this was Spitfire and Hurricane country.

      kind regards Peter

    • krillco profile image

      William E Krill Jr 4 years ago from Hollidaysburg, PA

      I'm hooked on your history pieces; once again, never heard of these innovative defenses. I'm wondering though, how obvious a target they were, though I suppose that from the height of the bombers, they made a pretty small target.

    • Peter Geekie profile image
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      Peter Geekie 4 years ago from Sittingbourne

      Dear scarytaff

      Thanks for your comments - yes I understand they were kept pretty well occupied dealing with the London bomber raids.

      Kind regards Peter

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      Derek James 4 years ago from South Wales

      Tremendous story, Peter. I knew of the forts but I didn't know there were so many. It must have been bristling out there. Voted up and interesting.

    • Peter Geekie profile image
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      Peter Geekie 4 years ago from Sittingbourne

      Dear teaches12345

      Thank you for your comments. It is surprising how many relics of war still exist and serve to remind us of the futility of mass killing.

      Kind regards Peter

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      Dianna Mendez 4 years ago

      Interesting read. I enjoyed reading the history and story on this. Thanks for the education.

    • Peter Geekie profile image
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      Peter Geekie 4 years ago from Sittingbourne

      Dear tillsontitan,

      They built some others for Liverpool but they never fired a shot in anger.

      Due to the success of the Thames Estuary forts similar designs were proposed to cover the approaches to New York but I don't know if they ever went beyond the planning stage.

      Kind regards Peter

    • tillsontitan profile image

      Mary Craig 4 years ago from New York

      How very interesting....I never knew about these 'forts'. One never knows what's going on in another country, especially years ago. Thanks for the education!

      Voted up and interesting.

    • Peter Geekie profile image
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      Peter Geekie 4 years ago from Sittingbourne

      Thanks Aethelthryth,

      I'm sure there is a whole story about the goings on of pirate radio v the establishment. I do have most of the details on file and just need the time to put it all together.

      Kind regards Peter

    • aethelthryth profile image

      aethelthryth 4 years ago from American Southwest

      Well, I guess there's a whole other story there! Maybe you should write a whole article about pirate radio stations, for the benefit of those in other parts of the world who had no idea there were such goings on?

    • Peter Geekie profile image
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      Peter Geekie 4 years ago from Sittingbourne

      Thank you for your comments Aethelthryth,

      In the UK in the 1960s the BBC had a monopoly on broadcasting and the only alternative we had was to listen to Radio Luxembourg which played some rather staid popular music. Most of the forts were outside of British territorial waters and what was called "pirate radio stations" were set up on them broadcasting music which the BBC would have considered " not suitable" and financing their operations by broadcasting advertisements. Just to add to their "cut throat" image the boarding of the forts and securing them to set up the transmitters was a pretty violent affair resulting in boarders being repelled with clubs and petrol bombs and in one instance a murder by shooting.

      The Government tried to starve them out by refusing provisions from the UK and court action against the advertisers and even military action. Eventually the pirate stations did not win but changed the face of rock music transmissions for ever. Many of our best DJs and TV and radio presenters started their career as a pirate station DJ.

      Kind regards Peter

    • aethelthryth profile image

      aethelthryth 4 years ago from American Southwest

      That's a fascinating story, or rather, set of stories! For those of us living a thousand miles from any sea, maybe you could explain what a pirate radio station is? I am picturing Blackbeard speaking into a microphone...