04EscapeShaft.jpg

This shaft is filled with gravel and goes down I believe to the second floor. In the event of an attack the main entrance was expected to be destroyed. In that event a lever could be pulled to open a chute to allow the gravel to pour down the shaft and fill a passageway. Once that was done a bulldozer was in place to move the gravel out of the way, then the occupants could reach the surface.