During World War II, this tunnel was filled with separate areas for officers and enlisted men and women. You can still see the divders’ brace points on the wall, the small brown iron strips. Each station had a telephone and about five feet to work with. It was crowded; in summer very hot, and in winter, very cold. It was in operation 24 hours a day. Right-click and choose "view image" to enlarge.
While on tour, I often wondered if the 19th century workers who dug this tunnel ever wondered how long it would be in use. If they only knew that they were digging the nerve center of British resistance 140 years later...