In this picture you can see the Langdon Searchlight Battery.
These Coastal Artillery Searchlights were built in WW2 to allow the illumination and identification of ships coming into an area of sea directly below the important cross-channel gun batteries. They are cut into the cliff face in Langdon Bay and are accessed by a passage hewn into the chalk. There were originally three emplacements, but the Western most one has been destroyed by a cliff fall. Unfortunately, the metal shutters in front of the surviving emplacements are rapidly deteriorating.