When the boys hit the beaches of Normandy 75 years ago, they created a shock wave that crashed through Europe. The subjects of two of my books felt that wave, Jim Stewart in Old Buckenham, England, and Audrey Hepburn-Ruston in Velp, the Netherlands. As much as we remember D-Day, as much as it’s celebrated, we simply can’t recreate or recapture the level of adrenalin felt anywhere on or near the European continent that particular day, Tuesday, June 6, 1944.

First came the anticipation. Everyone felt that, too; the tension, relentless and building—Allied forces in England, German forces in France, and the occupied peoples of France, Belgium, and the Netherlands. Where would the Allies attack? When would it happen? Word leaked out about Patton’s impressive First Army assembling in Kent. Not Patton, fretted the Germans. Anyone but Patton!

Tick, tick, tick. Time crept by. Minutes. Hours. Days. Weeks. March turned into April. April into May. As detailed in Mission: Jimmy Stewart and the Fight for Europe, brisk action in barracks pools at Jim’s 453rd Bomb Group and elsewhere handicapped where and when the invasion would finally take place. In 453^rd Operations, Jim knew the invasion was getting close because bombing missions by the group’s B-24s had transitioned from strategic flights against German cities and factories to tactical raids of key sites in France. It might be a railroad yard one day and a bridge the next, but the targets would be a couple hundred miles apart to reveal nothing about the intended invasion site. Would it be the Pas-de-Calais? Surely, yes, the shortest point between England and France. More daring gamblers said Normandy just because it was the last place Hitler would expect. For the Allied invaders, Normandy meant a long, torturous boat ride on choppy seas while rugged and heavily defended beaches awaited at the end.

A few hundred miles due east, the Dutch lived quite a different reality, as detailed in Dutch Girl: Audrey Hepburn and World War II. At age 15 and a junior member of the Resistance, Audrey was at this time helping downed Allied airmen avoid capture by day, while in the evening, dancing illegally to raise money for Jews in hiding. All the while her country experienced slow strangulation by ruling Nazi authorities who had extracted from the Netherlands all the food, coal, rubber, clothing, paper, and petrol they could in an ongoing effort to support the war effort on the Eastern Front. Dutch civilians had begun to suffer malnutrition that reached in and twisted bellies, all the while facing the anxiety of executions by firing squad for any random Resistance offense. By now, the Germans had confiscated radios from the Dutch—except for illegal sets that still operated on the sly. Officially sanctioned Nazi radio and newspaper reports boasted that invasion of the “Atlantic Wall” was no threat. According to the Germans, Allied attack was welcomed so the Americans and British could be defeated once and for all.

So the Dutch waited, hoped, and prayed. Every day those with radios listened secretly to regular broadcasts from Radio Oranje on the BBC. The Dutch listeners dared not speak the word that hung at the front of every mind: Liberation! If the day ever actually arrived, an Allied invasion would give hope to the hopeless, not just in small towns and large cities in the Netherlands but across occupied Belgium, throughout occupied France, and in all the concentration camps in Germany and Poland where Jews died by the day and Allied prisoners held out against disease and lice and inertia. In America, hope would spark through millions of mothers and fathers praying for the safe return of their children, the young people actually fighting this war.

If you watch The Longest Day, you get a sense of how the Germans on the Normandy coast felt when they beheld the invasion armada that misty dawn. If you watch Saving Private Ryan, you get horrifying glimpses of the killing machine the liberators faced on the beaches that day. And yet there’s no way history, let alone film, can do this day justice. As the news spread of military action at Normandy, as the titanic struggle played out on those beaches, as men fought and screamed and died, struggling dune to dune, hill to hill, hearts swelled in the United States and across Europe. Hands shook. Tears flowed. The free world held its breath through the longest day in history.

Seventy-five years later we can tour the beaches and imagine what the battle looked like. We can marvel at the crosses representing supreme sacrifice. We can revisit stirring eyewitness accounts. But we can’t feel the shock wave because it remains unimaginable. Jim was positioned to feel it in Operations at Old Buck when gates locked down and orders dictated what targets would be hit; Audrey felt it on a quiet street in Velp as secret radios barked out play by play and the Dutch dared hope they might break free of the oppressor.

What a day, that Tuesday in the fifth year of war—the day when everything changed, when the world felt a shock wave that tilted it in a new direction.