Gen. Dwight D. Eisenhower pulled few punches while addressing his troops ahead of the massive Allied invasion of France 70 years ago on Friday. The “German war machine,” he said, was fierce, well-trained, well-equipped and capable of fighting “savagely” — but not as strong as it once was.

“Our home fronts have given us an overwhelming superiority in weapons and munitions of war, and placed at our disposal great reserves of trained fighting men,” Eisenhower said. “The tide has turned! The free men of the world are marching together to victory!”

The resulting operation — D-Day — was a major turning point in World War II. Some 150,000 Allied troops landed that day on multiple beachheads in France to fight the Nazis, the largest amphibious military landing ever. By the end of the day, some 9,000 Allied soldiers were wounded or killed in action, but Eisenhower’s troops had established a foothold from which they could defeat Germany.

D-Day is one of the most celebrated military operations ever. Less known, however, is the secrecy and trickery the Allied forces used to improve the invasion’s chances of succeeding.

It was no minor thing: Operation Bodyguard, as it was known, even included pulling legendary Gen. George Patton from the battlefield in Italy to take charge of a fake army — with fake tanks and all — according to the Patton Museum Foundation. Eisenhower did so in an effort to get Hitler worrying about a possible Allied invasion of Pas de Calais, an area of northern France that was much closer to Allied strongholds across the English Channel in Great Britain.

A scholarly paper written in 1997 by an Air Force officer, Jon S. Wendell, breaks things down nicely. Bodyguard sought to convince Hitler of the following lies:

1. A combined British, American and Russian force would attack the Nazis in Norway in spring 1944. Hitler had seized control of Norway in 1940, deploying a large force there to hold ports in the area.

2. Allied forces would continue to press the “soft underbelly” of Europe, something they already had done in 1943.

3. If the Allies attempted any kind of invasion of France, it would be at Pas de Calais, but not before July. D-Day came nearly a full month before that.

4. Any kind of landings in  France would be an attempt to draw German force away of Pas de Calais, rather than the main effort.

A scholarly work by another Air Force officer adds that the United States also sent a man impersonating a four-star officer, Gen. Bernard Montgomery, to Gibraltar, at the mouth of the Mediterranean Sea, one week before D-Day. The thought was that the Germans would hear about the move and assume that a massive invasion on French beaches would not happen without Montgomery involved.

The truth, of course, was far different. Seventy years later, President Obama and other world leaders will gather on Friday on the beaches of Normandy to remember the heroism and sacrifices that were necessary to gain a major foothold needed to win the war.