In 1943, Naours became a key base for the army of occupation. The high command made of this quiet secluded place one of their best structures among their defensive installations as connected with the " Atlantic Wall ". Reinforcement, bricklaying, ventilation and lighting were achieved in the galleries, which were converted into collective or individual places, as needed, and fitted with the same equipment as used in submarines…
The whole site was devastated at the Liberation.

The underground city of Naours was open to the public in 1949 by Mr Raymond Martin.