Henry II spent 70% of the nation's treasure in order to build this castle in the 12th century. There is a good reason. Dover is only 22 miles from the French port of Calais. That means this is Britain's closest point to the continent. Any invading army would want to land at Dover first. This simple fact of geography makes Dover Castle the key to all of Great Britain.

No fighting in the war room!
~Dr Strangelove

It has been that way for centuries. During the Napoleonic wars, the British dug tunnels into the chalk cliffs at Dover to aid in the defenses. Those tunnels are still here today and were top secret until 1984. (There was discussion about using them as a Nuclear bomb shelter) It was during WWII, however, that the tunnels became vital.

After the fall of France in May 1940, it became necessary to evacuate the French and British military which had become surrounded at Dunkirk. Dover provided the main landing point for this operation.

Vice Admiral Ramsey directed the entire evacuation (Operation Dynamo) from these tunnels under the castle walls. It was estimated that only 45,000 soldiers could be evacuated. Instead, over 338,226 were brought back to Britian's shores which enabled them to fight again at another time. What could have been a disaster changed world history. Churchill called it a 'miracle'.