The Helfaut-Wizernes Dome

In the Pas-de-Calais department of northern France, close to the commune of Helfaut and Wizernes, lies a large Nazi bunker built during the Second World War. The most prominent feature of this bunker complex is an immense concrete dome, from which the complex derives its name—La Coupole, or “The Dome” in English. La Couple, codenamed “Bauvohaben 21”, was built to serve as a launch base for V-2 rockets directed against London and southern England, and is the earliest known precursor to modern underground missile silos still in existence.

The Helfaut-Wizernes Dome. Photo: CRM / Shutterstock.com

The V-2 was a revolutionary weapon. It was the world's first long-range guided ballistic missile powered by a liquid-propellant rocket engine. The rocket was developed as retaliation for the Allied bombings against German cities, although the V-2 program had begun in 1936, well before the war started. Standing 14 meters tall, the 12.5-ton rocket was fueled primarily by liquid oxygen and ethanol. Germany estimated that it would need large number of V-2 rockets and correspondingly, vast quantities of fuel, if it hoped to drive Britain out of the war. This meant that Germany had to ramp up production of liquid oxygen, and if possible, build new production sites close to the missile launching sites to reduce loss of propellant through evaporation.

The launch sites also needed to be close to the English Channel in northern France and Belgium, or in the coasts of the North Sea or in western Netherlands, because the V-2 missiles were of short range. The German Army wanted to use mobile firing batteries, as opposed to fixed launching sites, because they were less vulnerable to attacks. But Hitler, who was fond of huge, grandiose structures, ordered the construction of a massive bunker—a monolith-like structure now known as the Blockhaus d'Éperlecques—in the Forest of Éperlecques near Watten, north of Saint-Omer. But a bunker the size of Blockhaus d'Éperlecques was hard to hide. Soon Allied reconnaissance spotted it, and on August 1943, bombers wrecked the construction site before it could be completed.

Blockhaus d'Éperlecques in Watten. Photo: Zairon/Wikimedia Commons

The loss of Blockhaus d'Éperlecques forced the German Army to look for an alternative location for a launch site. They army had already taken possession of an old quarry south-west of Saint-Omer and some 12 kilometers south of the destroyed bunker. The quarry was being transformed into a missile storage depot where V-2s would be housed in tunnels bored into the chalk hillside before being transported for launching. Hitler ordered this old quarry to be converted into a vast bomb-proof underground complex with tunnels to accommodate workshops, storerooms, barracks, a hospital, and even a liquid oxygen manufacturing plant. The complex was to be topped by a large concrete dome, 5 meters thick and some 70 meters across, to protect it from Allied bombing.

Construction of the complex began in August 1943. An elaborate system of camouflage was installed on the hill top to conceal the dome. However, from photographs taken by reconnaissance aircraft, the Allied could tell that something was afoot, and decided that it was better to bomb now and ask later. The site was constantly bombed throughout its construction period. To overcome the challenges of carrying out work under a rain of bombs, the dome was constructed flat upon the ground, and the soil underneath was excavated so that workers could continue to work below protected under the dome. Additionally, the dome was surrounded by a bomb-proof skirt of reinforced concrete 2 meters thick.

Map showing the location of Bauvohaben 21, or the Helfaut-Wizernes Dome, and its primary target London.

Franz Xaver Dorsch, the chief engineer who designed the complex and oversaw its construction, planned a complicated system of railway network tunnels that could bring missiles and supplies into the heart of complex and transport them into storage galleries dug out into the chalk hill. When the time came, the rockets would be moved to a huge octagonal rocket-preparation chamber directly under the dome. This chamber was never completed but would have been 40 meters in diameter and up to 33 meters high. Rockets assembled in this chamber could exit through two tall passageways in vertical position and be transported by rail to two launchpads from where the missiles would be fired.

Wizernes site: reconstruction of Octagon. Photo: Sanders, T.R.B./Wikimedia Commons

Reconstructed probable plan of the main workings at the Wizernes site. Photo: Sanders, T.R.B./Wikimedia Commons

The Allied learned about the site’s true nature in March 1944, and renewed bombing with vigor. When conventional bombing failed to cause much damage, the RAF began using ground-penetrating Tallboy bombs, which completely wrecked the external construction works and buried the entrance to the tunnels with rocks and soil from the cliff face. The dome itself was surprisingly undamaged, and it still stands today. However, the damage to the tunnels made it impossible to continue working on the site. Eventually, Hitler realized his folly and abandoned plans for launching V-2s from bunkers. Shortly after, the Allied landed in Normandy and the area was liberated in September.

In 1997, the former bunker was converted into a World War 2 museum, focusing on the story of the V-weapons, life in occupied France, and the conquest of space after the war. The museum houses a large number of original artifacts including a V-1 and a V-2.

Satellite image of the area with the dome indicated by the arrow. Photo: Google Maps

An underground passage of the Bauvohaben 21. Photo: Vassil/Wikimedia Commons

The Helfaut-Wizernes Dome. Photo: Zairon/Wikimedia Commons