La Coupole - Design and Location

Design and Location

The successful attack against the Watten bunker forced the German Army to find an alternative location for a launch site nearby. They had already taken possession of an old quarry between the villages of Helfaut and Wizernes, south-west of Saint-Omer and some 12 kilometres (7.5 mi) south of the Watten bunker, near the Aa river alongside the Boulogne–Saint-Omer railway line, about three-quarters of a mile (1 km) from Wizernes station. The quarry had been designated for use as a missile storage depot where V-2s would be housed in tunnels bored into the chalk hillside before being transported for launching. The Germans undertook major work in August 1943 to lay extensive railway sidings to connect the quarry to the main line.

On 30 September 1943, Hitler met with Albert Speer, the Minister of Armaments and War Production, and Franz Xaver Dorsch, the chief engineer of the Todt Organisation, to discuss plans for a replacement for the out-of-commission Watten facility. Dorsch proposed to transform the Wizernes depot into a vast bomb-proof underground complex that would require a million tons of concrete to build. It would be constructed within a network of tunnels to be dug inside the hillside at the edge of the quarry. A concrete dome, 5 feet (1.5 m) thick, 71 metres (233 ft) in diameter and weighing 55,000 tons, would be built over the top of the central part of the facility to protect it from Allied bombing. Beneath it, about 7 kilometres (4.3 mi) of tunnels were to be dug into the chalk hillside to accommodate workshops, storerooms, fuel supplies, a LOX manufacturing plant, generators, barracks and a hospital.

A standard gauge railway tunnel, codenamed Ida, was to be built on a curving path that would connect it with both the east- and west-bound main line railway, allowing trains to run straight through the complex without needing to reverse or be turned around. This would serve as the main unloading station, where missiles and supplies would be offloaded onto trolleys that would transport them into the connecting galleries Mathilde and Hugo. Hugo connected in turn with Sophie, a dead-end railway tunnel branching from the main line into Ida. Each of the main tunnels had a number of unnamed side tunnels of the same dimensions as the main tunnels and up to 90 metres (300 ft) long. The central feature of the complex was a huge octagonal rocket-preparation chamber directly under the dome. It was never completed but would have been 41 metres (135 ft) in diameter and up to 33 metres (108 ft) high. A number of intermediate floors, possibly as many as ten, would have been built up the sides of the chamber.

The western side of the chamber opened onto two tall passageways called Gustav and Gretchen. Each was to have been protected by bomb-proof doors made of steel and concrete. The passageways were to be 4 metres (13 ft) wide and at least 17 metres (56 ft) high and were angled in a Y-shape, exiting into the quarry. Open-air platforms for launching rockets would have been at the end of each passageway. The two passageways were angled at 64° 50' and 99° 50' west of north respectively – not aligned with any probable target but merely permitting the rockets to be transported to sufficiently widely separated launch pads.

The facility was designed, as was its predecessor at Watten, to receive, process and launch V-2 rockets at a high rate. Trains carrying V-2s would enter the heart of the complex through the Ida rail tunnel, where they would be unloaded. A large number of V-2s could be stored in the side tunnels; LOX would also be produced on-site ready for use. When the time came, the rockets would be moved into the octagonal preparation chamber where they would be lifted to a vertical position for fueling and arming. From there they would be transported on motorised launch carriages, still in a vertical position, through the Gustav and Gretchen passageways. The launch pads were located at the end of the track on the floor of the quarry, from where the missiles would be fired.

The priority target for the V-2s was 188 kilometres (117 mi) away: London, which Hitler wanted to see pulverised by the end of 1943. The Allies were alarmed when an analyst found that part of the complex was aligned within half a degree of the Great Circle bearing on New York, and its equipment was large enough to accommodate a rocket twice the size of the V-2: the "America Rocket", the proposed A10 intercontinental ballistic missile.

Although physically separate, another facility built in nearby Roquetoire was an integral part of the Wizernes complex. Umspannwerk C was built to house a Leitstrahl radio command guidance system which could be used to send course corrections to missiles launched from Wizernes to fine-tune their trajectory during the launch phase.