The Long, Strange History of the Maunsell Sea Forts

Naval fortifications aren’t unusual in themselves. Land-based coastal artillery and forts to block enemy landings and bombardments have existed for centuries. In England, dozens still exist from the Napoleonic Wars and before, although they are now put to more peaceful uses. During World War II, British engineer Guy Maunsell gave this old idea a makeover. His forts were designed to destroy incoming enemy aircraft and, contrary to standard practice, they’d be sited out at sea. At a time of limited resources and unprecedented demand, the Maunsell sea forts could have been regarded as expensive white elephants of doubtful military value. They soon proved their worth.

The location of the forts was unusual: the Thames Estuary to protect London and the Mersey Estuary, guarding the vital convoy port of Liverpool. Unusual, perhaps, but entirely sound. Liverpool received countless convoys delivering the goods that Britain needed and that Roosevelt’s “great arsenal of democracy” could provide. Because of its location, Liverpool was quite vulnerable to bombers flying across England, then turning and attacking from the West. The Thames Estuary forts were directly on the Luftwaffe’s flight path to bomb London and industrial centers like the city of Birmingham.

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Maunsell designed two types of fort, which would be built on the coast and moved, virtually intact, to carefully chosen spots guaranteed to provide maximum protection. Innovative in concept and design, they were also heavily armed. Searchlights, heavy 3.75-inch quick-firing guns, and Bofors 40mm cannon initially gave Luftwaffe crews a nasty surprise, as they were located in the water, where no guns were expected. The Thames Estuary forts proved particularly effective.

Granted, the forts couldn’t completely stop mass raids, but by their installation in 1942, raids of that style were increasingly rare. The Germans’ defeat in the Battle of Britain and the worsening situation on the Eastern Front were becoming a sinkhole into which Luftwaffe resources, now increasingly scarce, disappeared. Luftwaffe commander Hermann Goering was also falling out of favor with Hitler for failing to defeat the RAF in 1940. Losing the Battle of Britain and then invading the Soviet Union forced Hitler into what he’d most wanted to avoid, fighting on two fronts. He was loath to forgive Goering’s failure and the resulting crisis.

Maunsell’s designs were innovative and came in two forms: Army and Navy. Navy forts were smaller and, as you’d expect, crewed by sailors. The Army forts had a more complicated design, comprising separate platforms linked by catwalks and carrying more guns than their naval counterparts. Most of the Army forts were concentrated off Liverpool while most Navy forts guarded against bombers attempting to use the Thames Estuary as a landmark for attacking London.

maunsell sea forts — The Thames forts
Photo Credit: Wikimedia Commons

The forts depended on supplies coming from the sea. Without regular deliveries of food, water, ammunition and rotating crewmen on and off duty, they’d have been useless. The Thames estuary forts also did far more than destroy incoming bombers. At the time, London had one of the largest dock complexes, making the Channel the world’s busiest shipping lane. German aircraft routinely tried to lay minefields in the area, but the Thames Estuary forts were there to hinder them.

Later in the war, Hitler’s Vergeltungswaffen (“vengeance weapons”) often flew over the forts toward London. Their guns could do nothing about the V2, a supersonic rocket and the world’s first ballistic missile. They could, however, pick off the slower, pulsejet-powered V1s nicknamed “buzz bombs” and “doodlebugs”. Efforts to stop V1s raining down on Central London were a top priority and the Thames forts destroyed over 30 of them along with 22 enemy aircraft. One fort’s gunners even destroyed an E-boat, despite not being designed to handle enemy torpedo boats.

With the war over, the forts became redundant. One by one, they were decommissioned and abandoned to crumble into the sea. Many were damaged by under-scouring, time and tide eroding the bedrock and steel legs supporting them. Saltwater steadily corroded the metal. One fort was demolished after a ship collided with it. One by one throughout the 1950s, the Maunsell sea forts were abandoned and mostly destroyed, but their story didn’t quite end there.

In the 1960s, pirate radio stations used some of the old forts as broadcasting stations. Pirate radio broadcasted their (usually rock) music illegally, without the proper licensing needed. Annoyed though the authorities were, there was nothing they could do as the forts were in international waters. That is, until the British territorial waters were extended–from including three miles offshore to a full 12. With the extension, the pirates lost their advantage and were quickly shut down.

The Liverpool forts were demolished in the 1950s, considered a danger to the shipping they’d once protected. Most of the surviving Thames forts are extremely hazardous to board, as they’re simply too badly damaged by the ravages of time and tide. Only a couple of the forts remain, and one of them, Fort Roughs (just outside British territorial waters) was taken over by pirate radio in the 1960s. It later declared itself an independent nation named Sealand. Granted, no government has ever recognized Sealand as an independent state and probably never will, but technically at least, it remains the world’s smallest independent island state.

In 2005, an artist named Stephen Turner took on a strange project. He decided to live in one of the remaining sea forts, Shivering Sands fort, for 36 days–the length of a typical tour of duty during World War II. Turner posted updates during his time to a website and later wrote a book about his experience alone on the waters.

Maunsell’s forts are long gone, as are most of the troops who once manned them. But they served their purpose well. They destroyed almost two full squadrons of bombers before they could hit London. Nearly thirty V1’s that would have caused great destruction (and killed countless Londoners) never reached their targets. Today the V2s, bombers, buzz bombs and most of the Maunsell sea forts reside permanently on the ocean bottom.

All told, they did far more than merely boost morale.

Featured photo: Steve Cadman / Flickr (CC)