(CBS News) With the anniversary of the 1944 D-Day invasion due this coming Thursday, there's an untold story that's coming to light about some of the soldiers who took part -- and we warn you, it's not an easy story to hear. Here's national security correspondent David Martin:
The Allied landing on the Normandy beaches marked the beginning of the end of World War II -- a conflict of such vast suffering as to defy comprehension.
"This is the greatest catastrophe in human history," said Pulitzer Prize-winning author Rick Atkinson. "There's 60 million people who die in World War II. It's a death every three seconds for six years."
In his new book about the liberation of Europe, "The Guns at Last Light," Atkinson quotes a German general as calling the battle for Normandy "a monstrous blood mill."
For the first 24 hours, General Dwight Eisenhower, the commander of Operation Overlord, did not know if his troops were winning or losing.
"Eisenhower had written a message accepting full responsibility for the failure of the landings," said Atkinson, "and he never had to use it."
Last weekend Defense Secretary Chuck Hagel read the words Eisenhower never used to the graduating class at West Point, as the standard for all who would lead: "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."
At stake was liberation from Nazi tyranny -- a heroic story, but one which had a dark underside.
Fifteen thousand French citizens were killed by Allied bombings leading up to D-Day.
Once the Allied forces were ashore, some GIs were left wondering whether they had liberated or obliterated French villages. The late Andy Rooney, who covered the invasion as a reporter, wrote of the French: "It was true they were being freed, but at the cost of everything they had."
And beyond that, not all American soldiers conducted themselves like members of the "Greatest Generation."
"War does bad things to people in general," said Atkinson. "It makes good soldiers do bad things, and it makes bad soldiers do terrible things."
"There is a great deal of war trauma, and as a result there was a great deal of alcoholism and just misbehavior," said Mary Louise Roberts. The author of "What Soldiers Do: Sex and the American GI in World War II France," she was the first American to gain access to French archives which had been sealed since the war.
Roberts photographed documents in which French officials complained of a "regime of terror" perpetrated by "bandits in uniform." Also, said Roberts, "There [were] many rape accusations on the part of the Norman women."
Atkinson came across similar documents.
"The French high command sends a letter to Eisenhower saying, 'Look, this is not acceptable. Our women are afraid to go out at night if they're unaccompanied,'" Atkinson said.
In response, Eisenhower ordered his commanders to take action against "the large incidence of crimes such as rape, murder, assault, robbery, housebreaking, etc."
But he still got letters from French mothers complaining that GIs were taking advantage of their daughters and leaving them pregnant.