The Turret Training Range.  Aircraft type gun turrets were situated at the landward side of the site.  The targets were mounted on motorized Wickham trolleys that moved around the edge of the range. The actual trolleys were protected by an earth and concrete wall, with only the target showing above.  Cliff erosion had moved the range right to the edge, indeed the base of the shed that used to house the trolleys is now on the beach below!
 1940s ATC Pages
 
An Island Images picture © Jon Wornham