Photograph by Alexandra Boulat

Beneath the highlands of Normandy, low tide widens the D-Day shore. On June 6, 1944, obstacles studded the sand as 200,000 Allied troops stormed Hitler's "Fortress Europe." The five invasion beaches encompassed some 45 miles (72 kilometers) of coastline. In this view, tucked in the distance, is the seaside town of Arromanches-les-Bains off Gold Beach, which was stormed by the British and became the site of the Mulberry harbor that served as an artificial port for Allied reinforcements and supplies. Farther east lies Juno Beach, taken by Canadian forces, and Sword Beach, scene of another British assault. To the west are the U.S. beaches of Utah and Omaha.

June 6 dawns, and D-Day once more returns to Normandy. The tide is low at Utah Beach and Omaha Beach, as it was then. The sand hardens underfoot, as it did then. I touch a rusted metal stump thrusting from the sand, a remnant of the rows of barriers that lined this shore on June 6, 1944. Clouds crowd the sky this morning. It will be a gray day, as it was then.

To this shore every June come clusters of silent men who walk with their kin and their memories. One of them is Joseph Vaghi, a warm, vigorous Navy veteran who was a beachmaster on D-Day—"a kind of traffic cop," he says—at a bloody stretch of Omaha Beach code-named Easy Red sector.

I met Vaghi on the wind-scoured bluffs overlooking those gray sands, now so empty and calm. Nearby was the American cemetery with its 9,387 graves, 23 of them carrying the names of men from Joe's outfit, the Sixth Naval Beach Battalion. Its men disabled mines, marked sea-lanes for landing craft, cared for the beachhead wounded under fire, and bore them through a reddening sea to evacuation craft. The day I met him, Vaghi was helping to dedicate a belated memorial to his fallen comrades. So humble was their outfit, he laughed, that the United States armed forces—even the Navy—forgot about them for nearly 60 years.

It was to meet men like Joe Vaghi, and to hear their stories, that I came to Normandy last summer. I was searching for the untold saga of D-Day, those fascinating bits of history and heroism that have gone largely unreported in the decades since that terrible morning on the beach. Many of these stories were lost because the sea closed over them, sealing lips forever. Others were obscured by the shroud of secrecy that was draped over many aspects of the invasion, including the Allies' Operation Neptune—the top secret naval and amphibious actions, under British command, that launched and supported the invasion.

As he and I talked, the U.S. Navy was again off the beaches of Normandy, this time to scan the seafloor. Using sonar, magnetometers, and the global positioning system, Navy archaeologists were filling in the gaps of history by locating the vessels lost while delivering the U.S., British, and Canadian troops who stormed the beaches and fought their way inland. Of the 5,300 ships, boats, and amphibious craft that took part in the invasion, at least 200 were lost on D-Day or during the perilous days that followed.

To piece together the full story, historians are now sifting through evidence ranging from recently declassified documents to underwater photos of the wrecks. What has emerged are secrets that men and women once guarded with their lives, adding detail and color to the story of D-Day. One of the darkest subplots of all, I found, came from the English side of the Channel.

For Joe Vaghi and tens of thousands of other Americans stationed in England in the spring of 1944, France was the Far Shore, the place where they would finally meet the Nazis in a fight to the death. To prepare, they trained along a stretch of English coast that had been cleared of civilians. It was called Slapton Sands, a tranquil beach that was chosen for its geographic similarity to the coast of Normandy. Their most realistic training was Exercise Tiger, a live-ammunition D-Day rehearsal that involved some 300 ships and 30,000 men in April 1944, six weeks before the invasion.

Gen. Dwight D. Eisenhower, supreme commander of Operation Overlord (Allied code for the invasion itself), was aboard an observers' ship on April 27, when Exercise Tiger went terribly wrong—failed air cover, late landing craft, confusion on the beachhead. Amphibious tanks, heading to shore, misaimed their guns and wounded soldiers on the beach. At least one of the tanks sank in choppy seas while its frantic crew managed to escape. Furious, Eisenhower returned to his headquarters, deeply worried about what the exercise augured for D-Day.

Worse was yet to come. Around 2 a.m. on April 28, nine German Schnellboote—fast, elusive torpedo boats—pounced on a line of eight U.S. tank-landing ships, or LSTs. They were churning down the English coast toward Slapton Sands, fully loaded with vehicles and men who were to land in the next phase of Exercise Tiger. German torpedoes struck three LSTs at the end of the line. LST-531 capsized and sank within minutes, taking hundreds of men down with her. The torpedo that hit LST- 289 crumpled her stern, but she stayed afloat and made it to port. Gasoline aboard LST-507 exploded and set the ship afire.

Eugene Eckstam, a medical officer on the 507, raced for the tank deck, which was filled with men and vehicles. "I saw only fire—a huge, roaring blast furnace," he later wrote. "Trucks were burning; gasoline was burning; and small-arms ammunition was exploding. Worst of all were the agonizing screams for help from the men trapped inside. But I knew there was no way I—or anyone else—could help them. I knew also that smoke inhalation would soon end their misery, so I closed the hatches into the tank deck and dogged them tightly shut."

Senior officers ashore, quickly assessing the damage, ordered the five surviving LSTs to continue steaming toward Dartmouth, their destination. Capt. John Doyle, commanding officer of LST-515, the lead ship, disobeyed the order. He turned back to look for survivors. "We started looking for the ones who were still alive," Brent Wahlberg, 515 gunnery officer, remembers. "We found 132 survivors." Many of the dead, they noticed, were floating head down, feet up, with their life belts inflated. No one had told them that the life belts were to be worn under the armpits, not around the waist. That lesson from Exercise Tiger would be taught to invasion troops, saving countless lives.

In the meantime, Eisenhower had an intelligence nightmare on his hands. To keep the disaster a secret, he ordered extraordinary measures and kept the lid so tight that the details remained unknown for many years. He did not want Germany or Allied troops to know about the huge loss of life—749 sailors and soldiers by final count. Of even greater concern was the possibility that the Schnellboote might have picked up survivors who carried the most closely guarded secret of the war in their pockets—the location of the D-Day landing.

One simple word, BIGOT, is stamped in big letters across the Operation Neptune Initial Joint Plan of February 12, 1944, and from then until June 6, that stamp appeared on all supremely secret pieces of paper handled by D-Day planners. If any of those papers or maps had fallen into enemy hands, the invasion would have failed or been scuttled—a distinct possibility in the anxious days after Exercise Tiger.

BIGOT was a code word within a code word, a security classification beyond Top Secret. When planners adopted Neptune as the code word for the naval and amphibious aspects of the invasion, they realized that greater protection had to be given to any document or map that even hinted at the time and place of D-Day. They chose the odd code word BIGOT by reversing the letters of two words—To Gib—that had been stamped on the papers of officers going to Gibraltar for the invasion of North Africa in November 1942.

Those who were to get date-and-place information were given special security back-ground checks. If they qualified, they were described as "Bigoted." So when Eisenhower learned about the catastrophe off Slapton Sands, he wanted to know whether any of the dead or missing had been Bigoted. About ten men had. Those bodies were found and their documents collected. But had the Germans found any secrets on other bodies?

Allied code breakers, who eavesdropped on German communications, listened for days to determine whether the Germans had gained any new intelligence about D-Day. They had not. D-Day's secrets were still safe.