Seventy-one years ago today the Imperial Japanese Navy launched a devastating, surprise attack against American naval forces at Pearl Harbor. That moment became the defining memory marker of a generation—much as the Kenney assassination and 9/11 would become for later generations. Everyone of age to understand that Sunday morning would always remember where he or she was when the news crackled out of a radio or sprawled across the front page of a newspaper.

On that day, December 7, 1941, Europe was fighting Nazi Germany and President Franklin D. Roosevelt was slowly preparing the United States for an inevitable entry into the conflict. But America was still divided; many held strong isolationist views. Roosevelt had been slowly chipping away at American isolationism for years, but in two hours on a quiet Sunday morning, Japan finished his task.

The magnitude of Japan’s attack was sobering, but it was the long-planned, secretive manner in which it was executed that truly enraged the American people. America suddenly stood united in purpose as never before.

At Pearl Harbor that morning, America lost eight battleships, hundreds of airplanes, and 2,400 navy, marine, army, and civilian personnel. The memories of those lost that day are sacred, but no less so than the contributions of those who answered the call in response. Over the next four years, 8 million American men and women would serve in the armed forces.

Today, those who remain are in their late eighties and nineties. They have many memories of long and fulfilling lives, but in the twilight of their years so many of their sharpest memories seem to be of that time long ago when as fresh-faced teenagers they gave their all to a common purpose. Much has been written about their leaders, but it was their individual efforts that made this difference.

Perhaps the greatest lesson of Pearl Harbor is that nothing is impossible for the American people.

The most amazing transformation in American history may be the 1,366 days between December 7, 1941, and September 2, 1945—and the speed with which the Axis powers were reduced to ruin once the United States entered the Second World War. During this time, the tremendous outpouring of America’s industrial strength in ships, planes, tanks, and other armaments was exceeded only by the bravery and determination of the nation’s men and women.

They were a “can-do” generation who did not take “no” for an answer. They did not put off until tomorrow what needed to be done today. We should remember their resolve, honor their commitment, and seek to emulate their example. They truly were the greatest generation.