Steven J. Zaloga 
D-Day Fortifications in Normandy [PDF ebook] 

German defenses along the Normandy beaches were part of the larger Atlantic Wall fortifications designed to defend Fortress Europe. When Field Marshal Erwin Rommel took command of the invasion front in late 1943, he began a program to enhance fortifications along the Normandy coast as he believed that any Allied assault had to be stopped on the invasion beaches themselves. His most important contribution to the defenses was an extensive program of improvised beach obstructions to complicate any landing attempt. This book analyses these fortifications and describes how the Allied forces overcame them on the morning of June 6, 1944.