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Normandy veterans gather for a memorial service in Ranville War Cemetery on June 5, 2013 near Caen, France. Across Normandy several hundred of the surviving veterans of the Normandy campaign are gathering to commemorate the 69th anniversary of the D-Day landings which eventually led to the Allied liberation of France in 1944.(Photo by Matt Cardy/Getty Images)

It is not often that we use these pages to mark the 69th anniversary of anything, but today is an exception. It was that number of years ago -- on June 6, 1944 -- that 156,000 American, British and Canadian troops participated in Operation Overlord, better known as D-Day.

The mass invasion of the beaches at Normandy, France, was a seminal moment in the eventual victory by the Allies in World War II.

Many of us are not old enough to remember that battle or even that war, but those who are often correctly remind us that we should never forget the courage and heroism displayed during that horrific battle and the sacrifices that were made during that war so that we can live in freedom.

It seems somehow bitterly ironic that this week also saw the passing of the last World War II veteran serving in the U.S. Senate. Sen. Frank R. Lautenberg, D-N.J., died Monday.

In the not-too-distant past there were many senators who had served in the armed forces during World War II. Names such as Bob Dole, John Warner, Phil Hart, Ted Stevens, Daniel Inouye and Ernest Hollings roamed the Senate's hallowed halls.

They are all gone now; Lautenberg was the last of the 115 members of the Senate who had served in the military during World War II.

But there are still people who do remember that time vividly and they tell us of an era when everyone in the nation pitched in and did something. Even those who didn't go into battle sacrificed in many ways. Such sacrifice wasn't considered heroic, it was the norm. One could fairly argue that never has the United States been so united as it was during World War II.

By all accounts, that invasion 69 years ago was nothing short of hell and it took a devastating toll.

Research by the U.S. National D-Day Memorial Foundation estimates that more than 4,400 Allied personnel -- about 2,500 Americans -- were killed during the battles surrounding the invasion. Thousands more suffered devastating injuries. Such is the tragedy of war.

But that bloody day, so many years ago, changed everything. The success of D-Day has often been called the beginning of the end of World War II. We should be grateful to all of those who fought and sacrificed on our behalf. To them and their families, on this anniversary, we offer a sincere thank you.