This Google Earth image shows the imposing layout of the defenses and gives some perspective. (click to enlarge)
Longue sur Mer as seen from Google Earth
I also dug up from the web an old plan of the original layout (in French) showing mine fields (mines), barbed wire (barbelas), trenches (tranchees), tobruks (tobrouk), shelters (abris), and munitions storage (soutes).
Original Longue Battery plan
Here is a small excert from Stephen Ambrose's D-Day about Longue.
Excerpt from D-day about the Longue battery
Here is the layout of the four guns of Longues as Redington I visited them.
The concrete was barely touched by shelling. (Redington on top)
This gun's in pretty good shape. Redington explained to me the purpose of the 'stepped' opening of the gun placements. They could not be smooth as this would guide or funnel the incoming shells into the placement. Instead they are stepped so incoming rounds impact and detonate outside. You can see where one struck above and to the left of Redington's head in the picture below.
Redington and the big gun
View of Gun Placements. Notice the dimples in the earth. These are crater remanants from naval shelling and bombing.
In D-Day Ambrose relates the story of the unlucky battery shown below. It was in an artillery duel with the USS Arkansas when a shell struck the gun apparently as it was being loaded. The gun barrel exploded into 3 pieces. It also happened that the doors 3 floors down to the powder magazine were all open and that exploded too. The destruction as you can see was massive and complete. The commandos that later captured this installation reported no signs of human occupation remained, the explosion was so complete.
Destroyed Gun Placement
Observation and Fire Control Station
It was interesting to see at the Tobruk below that the German who constructed it personalized it with a drawing of horses (one that appears to be hung, well, like a horse). He signed his name in the upper right as PM Uttz, Dec 6, 1942
A tobruk is a German defense installation named after the Libyan town where it was invented in WWII.
Tobruk with Horse inscription
Inside of a Tobruk (click for video)