Key point: They were doomed no matter what.
General Dwight D. Eisenhower's face was grim but composed as he read a short message to the assembled group of reporters on the morning of June 7, 1944.
"Our landings in the Cherbourg-Havre area have failed to gain a satisfactory foothold and I have withdrawn the troops. My decision to attack at this time and place was based upon the best information available. The troops, the air and the navy did all that bravery and devotion to duty could do. If any blame or fault attaches to the attempt, it is mine alone."
Eisenhower never actually uttered these words. But he did scribble them down in the tense days before the Normandy invasion. Despite the years of planning for D-Day, and the awesome armada of men, ships and planes that he commanded, Eisenhower knew how risky it was to storm ashore into the heart of Hitler's Atlantic Wall.
With seventy years of hindsight, it is easy to assume that by June 1944, the Third Reich was doomed. Russian armies were relentlessly advancing from the East; Anglo-American armies were invading from the West, while German cities and factories burned under around-the-clock attacks by American and British bombers.
But those who fought the Germans knew better than to underestimate them.
As Eisenhower contemplated the assault on Hitler's Fortress Europe in the hours before D-Day, he knew how dangerous the operation was.
D-Day was a success. But here are five ways that D-Day could have ended in disaster:
The Germans could have learned the location of the invasion. By early 1944, everyone knew the invasion would soon be coming. British civilians knew, as they watched their island practically sink under the weight of division after division of American troops. Hitler also knew, which is why he transferred his elite panzer divisions from the Eastern Front to the West.
The big question wasn't if the Allies would come, but where. Control of the seas gave the Allies immense flexibility in picking an invasion site, which meant the Germans had to be prepared for landings anywhere from France, to Belgium, to the Netherlands (Hitler was even convinced there would be a landing in Norway).