This is one side of the "Mechanical Signaling System" used to give information to the gunnery crews. The oval shape to the left is apparently a cast concrete megaphone. This is one leg of a "Y" shaped structure and there's a mirror image of this on the other side leg to signal the other gun pit. The numbers were changed by cranking a wheel inside the building at the base of the "Y". The numbers provided the Elevation and Azimuth for the gun crews. And the mechanical gears still work.
Photo album created with Web Album Generator