Dover has been used as a point of English fortification. During the Napoleonic Wars, the English began building a series of tunnels on the castle grounds to keep troops and defend England in the event of a French invasion. (Calais, France is directly across the Channel from Dover) These tunnels were expanded during WWII and it was from these tunnels that Admiral Ramsay coordinated the "Miracle at Dunkirk," or rather the successful evacuation of nearly defeated Allied forces from the European mainland (1940). The Dover-Calais corner was known as "Hellfire Corner" so the tunnels also served as a dressing hospital and dormitory for all downed airmen. I took a tour of this extensive complex, but could not take pictures, so this one is the only one I have.