Visiting the Fan Bay Plotting Room
Hidden beneath the White Cliffs at Fan Bay lies one of the most remarkable surviving Second World War sites in Britain. Built on the orders of Prime Minister Winston Churchill, Fan Bay Battery was the first of a chain of coastal artillery batteries constructed to defend Britain from invasion attempts and restrict enemy shipping movements in the Dover Strait. Deep underground, the Plotting Room housed advanced electromechanical equipment that calculated how the battery's guns should be aimed. Today, you can explore this once top-secret bunker and discover the vital role it played in Britain's wartime defence.
The Fan Bay Battery
Fan Bay Battery consisted of three 6-inch guns positioned high above the Strait of Dover. As the first of seven major artillery batteries built around Dover, it formed part of a network designed to protect one of Britain's most strategically important waterways.
Accurately engaging moving targets at sea required a level of precision rarely seen in land-based artillery. To achieve this, information from observation posts, radar stations and other military sites was collected and processed underground in the Plotting Room. The resulting calculations were then relayed to the gun crews, enabling them to aim with remarkable accuracy.
Because of its importance, the Plotting Room was a heavily protected and highly secret installation. Few people knew it existed, and even fewer were permitted inside. To book your guided tour ticket, please visit our event pages for November / December and January / February 2027
Building the Plotting Room
Construction began in early 1941. A large excavation was dug into the chalk before reinforced concrete and brick walls were built. The structure was then covered with a massive concrete roof and buried beneath layers of earth, leaving only the access shafts and ventilation cowls visible.
Miles of underground cables linked the bunker to the guns, observation posts, radar stations and Fortress Command. By late summer 1941, the Plotting Room was fully operational.
Inside the bunker
The underground complex contained:
- Entrance lobby
- Battery Command Post
- Guard rooms
- Airlock
- Plotting Room
- Ventilation room
- Cable and drainage duct
- Emergency escape tunnel and shaft
Heavy steel doors, gas-tight features and emergency escape routes reflected the strategic importance of the site and the need to keep personnel safe during attack.
How it worked
Unlike the plotting rooms often portrayed in wartime films, the facility at Fan Bay did not rely on map tables and model ships/aircraft. Instead, it housed sophisticated electromechanical equipment adapted from naval fire-control systems.
Information about enemy targets, weather conditions and other variables was fed into the system, which calculated the precise bearing and elevation required for each gun. The results were transmitted electrically directly to the gun crews, who adjusted their weapons accordingly before opening fire.
The success of this technology led to similar systems being installed at other coastal batteries around Britain.
After the War
Although the guns were removed in 1952, the bunker was retained during the early years of the Cold War in case it was needed again.
By 1963, however, the site had become obsolete. The remaining equipment was destroyed, the access points sealed and the land returned to agricultural use. Later clearance works buried what remained of the site, and the Plotting Room disappeared from view.
For nearly half a century, it remained hidden beneath the landscape.
Rediscovery
After the National Trust acquired the site in 2017, volunteers and staff began searching for the lost bunker. Careful research using historic maps and plans helped identify the likely location of the emergency escape shaft. In December 2017, excavation revealed the original escape hatch, still intact. When it was opened, volunteers discovered an extraordinary time capsule, untouched since the 1960s.
Following extensive conservation work, much of it carried out by volunteers, the Plotting Room opens to visitors in November 2026, allowing a new generation to experience this unique piece of wartime history.
Visiting the Plotting Room
Please park at our additional parking facility. The entrance is at www.what3words.com/fidelity.book.approve, opposite the entrance to Sherley's Farm on Upper Road - postcode CT15 6HY. After parking, you will be escorted by one of our guides to the Plotting Room site. Before entering the bunker, you will be issued with a hard hat and head torch.
The guided tour takes you underground to explore the access shaft, Battery Command Post, guard rooms, airlock, plotting room and ventilation room. You'll also see the emergency escape shaft and the entrance to the drainage duct. Along the way, you will see original wartime notices, surviving decorations created by those who worked there and many of the features that helped keep the bunker operational.
Your guide will explain how information was gathered and processed, how the equipment worked and how commands were relayed to the guns. You will also learn about the extensive precautions designed to protect personnel in the event of a gas attack.
Tours last approximately 40 minutes. To book your tickets please visit the following pages: November / December and January / February 2027.
Please see our video and Frequently Asked Questions below for additional information before your visit.
Plotting Room experience 3D visualisation
Join us for an exciting 2-minute LIDAR preview of the Fan Bay Plotting Room. Video: ©National Trust/University for the Creative Arts.
This video is hosted by YouTube