The Normandy peninsula was a possibility. But the obvious candidate was the Pas-de-Calais region, just twenty miles across the English Channel from the cliffs of Dover. The Germans kept many of their troops around Calais, and the Allies happily encouraged them to do so. They even created a fake army—commanded by George Patton—that appeared poised for a Calais invasion. The result was that the Germans maintained substantial forces in Pas-de-Calais for months, convinced that Normandy was just a decoy landing. Meanwhile, their armies in Normandy were relentlessly chewed up until the Allies achieved a breakthrough in August that took them all the way to Germany.

It could have turned out differently. Perhaps the Germans might have guessed that Normandy was the real invasion site. Perhaps a German spy in England had managed to penetrate Allied security. A careless word, a stolen document…there were so many ways that the secret of D-Day might have been compromised.

Whatever the reason, the result would have been catastrophic. German defenses would have been strengthened; every beach would have become a kill zone like Omaha Beach, where the first waves of U.S. soldiers were almost wiped out.

But the death blow to D-Day would have been the panzer divisions massing in Normandy to drive the invaders into the sea.