The Maunsell Forts: wartime towers in the North Sea
Marek Halden
Updated 24 September 2026
8 min read
Thames and Mersey estuaries, England
The Maunsell Forts are among the strangest structures Britain ever built: towers on stilts, standing in the open sea, designed to shoot down German bombers. They were named after their designer, Guy Maunsell, and they were operated as army and navy forts in the estuaries of the Thames and the Mersey. The war ended, the forts were abandoned, and they are still out there.
Forts on stilts
As German aircraft laid mines and attacked shipping in the Thames estuary in 1942, the Royal Navy and the Army needed a way to defend the approaches to London and the great ports. Guy Maunsell, a civil engineer, designed forts that could be towed out to sea and sunk onto the seabed, with their guns and crews raised above the water on concrete and steel legs.
Four navy forts and six army forts were built. The army forts, like those at Red Sands and Shivering Sands, were clusters of towers joined by walkways, each carrying anti-aircraft guns, radar and accommodation for dozens of men. They were towed into position during the war and manned in some of the most exposed conditions imaginable.
Abandoned, then occupied
The forts were decommissioned in the late 1950s, and their crews came ashore for good. Left to the sea and the weather, they began to decay — but they did not disappear. In the 1960s some of them found a new and unexpected use as bases for pirate radio stations, broadcasting pop music to Britain from international waters beyond the reach of the law.
One fort, Roughs Tower, was occupied in 1967 and declared the independent Principality of Sealand, which still claims sovereignty today. Others were used for radio, for broadcasting, and, in time, for little at all. The sea has been patient with them, and their rusting silhouettes have become a familiar sight to sailors and a favourite subject for photographers.
Towers in the tide
Today the surviving Maunsell Forts stand as some of the most evocative ruins in Britain. They are too far offshore to visit easily, and the sea is dangerous, but they can be seen from the coast and from boats, and they have come to stand for a whole aesthetic of decay and transience — the idea of a machine left to the elements.
They are a different kind of abandonment from the towns and hospitals elsewhere in this archive: not a place people lived, but a machine built for a single purpose and then simply switched off. Like the Cold War listening station on Teufelsberg in Berlin, they are military hardware that outlived the war it was built for.
About the Maunsell Forts
The forts stand in open water and are not open to the public. They can be seen from the coast and from boats.
- Do not attempt to land on or board the forts; they are unsafe and the sea is dangerous.
- The best views are from the shore and from organised boat trips.
- Respect the forts as heritage — several are protected structures.
Frequently asked questions
What are the Maunsell Forts?
Second World War defensive towers built in the Thames and Mersey estuaries, designed by Guy Maunsell.
Where are the Maunsell Forts?
In the Thames estuary off the east coast of England and in the Mersey estuary in the northwest.
When were the Maunsell Forts abandoned?
They were decommissioned in the late 1950s, though some were later used for pirate radio.
Can you visit the Maunsell Forts?
No. They are offshore and unsafe; they can be viewed from the coast or from boats.
Related places
If this one stayed with you, these entries sit in the same corner of the archive:
- Dülmen-Visbeck: the Cold War bunker under a quiet field — Germany
- Teufelsberg: the spy station built on a hill of rubble — Germany
- Hashima: the island that ran out of people — Japan
Marek Halden
Marek Halden has been photographing and researching abandoned places since 2019, working legally and leaving every site as found. This archive records architecture, history and the human stories behind the walls — and never encourages trespassing.