The Copula war museum - La Coupole, Saint-Omer

During WW2, the Nazis wanted to bomb London with V2 rockets launched from the north of France. This rockets were fuelled with liquid oxygen. So, in order to reduce the losses of that precious fuel during its transportation, the Nazis decided to build huge bomb-proof assembly and launch facilities close to Saint-Omer city...
Thus, work on the La Coupole was begun after the nearby Éperlecques bunker factory had been damaged by Operation Crossbow bombing.
In January 1944, an enormous concrete dome, or cupola, was built over the top of the facility, giving the site its name. The dome was 71 m in diameter, 5 m thick and weighing an estimated 55 000 tonnes.
Following Allied bombing in June 1944 that severely damaged the site, it was closed down in July 1944 before it was completed and before it had fired a rocket.