In order to house the troops and store munitions, the Germans built about a dozen underground shelters on the site (models type SK) with walls built of concrete or stone, 50cm thick. These shelters were equipped with wooden doors and fitted out with a heating system, with a splinter screen wall and emergency exits which, in certain cases, were used as light wells and airshafts. No bunker possessed a ventilation system or protection against gas. The lack of a ventilation system is explained by the fact that the garrison living in the bunkers (on average about a dozen men per shelter) had to return to their combat posts equipped with their gas masks, in the case of a gas attack.
