Thursday, June 6, 2013, marks the 69th anniversary of D-Day, the momentous invasion of Normandy, France, by the Allied Forces during World War II.

History Associate Professor Aaron Gillette provides a better look at the largest amphibious invasion in world history.

Question: How were the Allies able to conduct such a massive attack without Germany becoming aware of the plans ahead of time?

Gillette: To mislead the Germans as to when and where the invasion would take place, the Allies carried out a massive and very successful deception campaign. They convinced the Germans that the invasion of France would actually be at Pas-de-Calais, 150 miles to the east of Normandy. The Allies created an imaginary "First United States Army Group" led by General George Patton. Phony radio traffic was produced solely for the Germans to intercept, mock airplanes and ships were used to make Patton's army seem real, and double agents conveyed deceptive information about the landing site.

Question: In addition to the deception tactics, what are some of the reasons the Allied forces were successful at Normandy?

Gillette: One day before the invasion, the Allied commanders were worried that poor weather would force the invasion to be called off. Because that would cause a multitude of problems, the Allied commanders reluctantly kept the invasion date for June 6. In actuality, this turned out to be very beneficial to the Allies because the German defenders concluded that there was no way the Allies would try to invade France in such unfavorable weather, and so were unprepared for the invasion. The overall German commander, Erwin Rommel, even returned to Germany for his wife's birthday party.

Question: Despite all of these advantages, the Allies were almost defeated at Normandy, correct?

Gillette: At the American landing site in Normandy, codenamed "Omaha Beach," the massacre of U.S. troops was so brutal that the invasion was almost called off. For example, 16 tanks were offloaded onto the beach that day—only two survived the first few minutes of the attack. The official Allied report later stated that "within 10 minutes of the ramps being lowered [for the troops to hit the beach], [the leading] company had become inert, leaderless and almost incapable of action. Every officer and sergeant had been killed or wounded [...] It had become a struggle for survival and rescue." The scene is quite accurately depicted in the movie "Saving Private Ryan."

However, over the next few weeks the Allies overcame the defenders, and began their drive towards Germany.

Question: What was Hitler's response to the invasion?

Gillette: Command of the defending troops was very poorly organized and they had to await Hitler's direct orders before they could maneuver to counter the invasion. However, when the invasion began in the early morning hours, Hitler's staff refused to wake him up so early, and many German troops had to wait until the Fuehrer got out of bed before they were allowed to move into action.

The Allied deception plans were so successful, and Hitler so stubborn, that he remained convinced for seven weeks after the Normandy landings that these were just diversionary tactics, and the real invasion had yet to occur at Pas-de-Calais. Because of this, Hitler refused to allow his best troops to be sent to Normandy to fight against the real invasion until it was too late.

For more information on the D-Day invasion, check out the History Channel's website here.