La Coupole is an underground complex in the French commune of Helfaut (Pas-de-Calais department). Built during World War II, it was intended for the storage and launch preparation of 500 V2 rockets (50 rockets per 24 hours). The site was chosen because of its location along the Calais-Boulogne-sur-Mer railway line.

The construction of the installations was discovered through aerial photographs, after which the Allies began heavily bombing the area as part of Operation Crossbow. The RAF carried out repeated air raids during the last five months of La Coupole's construction. During the bombing raids, which dropped over 3,000 tons of bombs, 55 people were killed in the village of Helfaut 21 and the neighboring municipality of Wizernes. The Tallboy, a bomb weighing over 5 tons, was dropped twice.  The Nazis realized the installation was too vulnerable and decided to launch V2s from mobile platforms. Therefore, the base was never put into use. Construction work was halted in July 1944. The dome and 7 km of underground tunnels were now complete.

https://lacoupole-france.com/nl/