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There is a Osprey book on this subject here's the link.

http://www.ospreypublishing.com/titl...=S5562~ser=FOR

The link is a bit slow so here's the details.

U-Boat Bases and Bunkers 1941–45
(Fortress 3)

Author: Gordon Williamson
Illustrator: Ian Palmer

US Price: $16.95
UK Price: £11.50
Canadian Price: $23.95

Availability: In stock


Paperback; February 19 2003; 64 pages; ISBN: 1841765562


About this book
Few of the massive military structures built by Germany during World War II are as impressive as the U-Boat bases and bunkers in Germany, Norway and France. This title takes a close look at the formidable edifices on the French coast (Brest, Lorient, St Nazaire, La Pallice, Bordeaux) in Norway (Bergen, Trondheim) and Germany (Keil, Hamburg, Helgoland) and also focuses on the huge 'Valentin' factory complex at Bremen, which manufactured the new type XXI electro-boats. Bunker protective systems, such as camouflage, light and heavy flak installations and nearby air cover, are also examined as well as resident flotillas and the fate of the bases at war's end.

Contents
Introduction
Chronology
Design and Development
Tour of the Sites
The Principles of Defense
The Living Sites
Operational History
Aftermath
The Sites Today
Bibliography and Further Reading
Glossary
Index