If you have seen "The Longest Day" movie, then the bunker that the German officer goes to with his dog and watches for the invasion is either THE actual fire control bunker or one just like it. It was on a cliff, looking out to sea. The actual battery was 4 casemated guns which were positioned I think a full mile or so behind the fire control bunker. They were on flat ground but had dirt pushed up behind to make them look like barrows of sorts. The battery and fire control bunker still exist. Of the four gun positons, one still has its gun and gunshield and there are lots of pictures of it floating around of that.
Please look at this site for positions from above. Good photos.
More good photos.