La Coupole (the cupola), between the villages of Helfaut and Wizernes in northern France, 5 km. from the city of St Omer is important for its role in the Second World War, as an example of concrete construction, and for its influence on the space programmes of the second half of the twentieth century.
The dome is located in a former chalk quarry. It was built as Bauvorhaben 21 (Building Project 21) or Schotterwerk Nordwest (the north-west gravel works) from 1943 as a base from which Nazi forces could launch the new V2 rockets towards London. The dome, designed by Werner Flos, is 71 m. in diameter, 5.1 m. thick, and consumed 55,000 tonnes of concrete. Much of the construction work was carried out by forced labour. Beneath the dome extended some 7 km. of tunnels, which were built to dimensions sufficient to accommodate much larger rockets than the V2, which might have been capable of reaching the United States. It was the prototype for other missile-launching silos, both those constructed for military purposes during the Cold War and those used in space exploration programmes. The site was linked to the railway from St Omer to Boulogne. The base was never used for its intended purposes as a result of bombing by the RAF and the USAAF. Many raids were unsuccessful but on 17 July 1944 most of the entrances to the tunnels were blocked, although the dome remained intact.
After the installation was captured by Allied forces in September 1944 some structures were demolished but it was then abandoned. The site was acquired by the local government authority in 1993-94 and was opened in 1997 as a museum which features the Nazi occupation of France, the history of the V-weapons and the development of space exploration. Ida, the one tunnel that was left intact after the bombing, provides access to the underground installations. In 2012 a planetarium was opened which provides a 50-minute 3-dimensional cinema programme.
The managers of La Coupole are also responsible for the nearby Fortress of Mimoyecques, intended as a base for another Nazi secret weapon, the V3 cannon which was intended to fire relatively small missiles in rapid succession toward London. Like La Coupole, it was never brought into use, having been heavily damaged by bombing in July 1944 before being captured by the Canadian army the following September. The site has been preserved as a museum since 1984.