By the spring of 1942, Hitler had made a fortress of Europe, and the Allies began to plan the biggest invasion in military history. The history-altering success of the D-Day Invasion depended on innovative engineering and technological advances. This... (more) is the story of those scientific and mechanical breakthroughs--the overwhelming array of landing craft, specialized weapons, and ingenious electronics--used to breach Fortress Europe on June 6, 1944.