La Coupole

La Coupole, also known as the Coupole d'Helfaut-Wizernes and originally codenamed Bauvorhaben 21 or Schotterwerk Nordwest, is a Second World War bunker complex in the Pas-de-Calais department of northern France, about 5 kilometres from Saint-Omer, and some 14.4 kilometers south-southeast from the less developed Blockhaus d'Eperlecques V-2 launch installation in the same area. It was built by the forces of Nazi Germany between 1943 and 1944 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.

Constructed in the side of a disused chalk quarry, the most prominent feature of the complex is an immense concrete dome, to which its modern name refers. It was built above a network of tunnels housing storage areas, launch facilities and crew quarters.

Source: Wikipedia