I'll soon be resuming work on a 1:72 German U-boat bunker that I started quite some time back, and still have not found near all of the references I'd like to have on the bunkers themselves. I already have an after the battle volume, Sutton and Osprey books on bases (OK), as well as the Schiffer volume on the bunkers, but none is as detailed as I'd really like. Can anyone recommend a book that has great photo coverage of the bunkers?

I'm not seeking photos from any one specific bunker location, but rather an overview, showing lots of details.