Yorkslass, it does look a bit like a WW2 bunker/observation tower similar to the kind you find on Jersey, and I can 'see' something which appears to be a jetty coming out into the sea, possibly for access purposes.
But the photo is older, and if you wanted to build a bunker/observation point then why put it where the sea will cause you problems rather than put it on top of the cliff - where the view would be better anyway?
I think it is just more rocks which happen to look like something man made in the lighting conditions and from this particular viewing angle.