This complex of bunkers on the grounds of the Chateau de Pignerolle, comprised the communication centre for the U-Boat campaign during WW2. I was unaware of this complex until I recently saw it in a PBS program called 'Nazi Mega Weapons' (what a terrible title!) There are at least ten bunkers in the complex including the main one; it is connected the Chateau H.Q. by a tunnel under the gardens. Curiously I am unable to find very much information in English, only French.