Why did the Allies attack on D-Day?- How did the Allies pick Normandy as a target?- What was Operation Overload, the second front against the Nazis? June 6, 1944: D-Day was a deciding conflict in World War II. But the invasion was not a straightforward attack. From feeding Nazi spies false information on the attack to developing new technology like the Mulberry harbours, D-Day changed the course of the War for good. The Largest SeaBorne Invasion In History. Written by historian, author, and broadcaster James Holland, D-DAY 1944 is an essential introduction to the naval invasion that began the liberation of Western Europe from the Nazis.