Seventy-five years ago Thursday, a battalion of elite U.S. Army Rangers scaled the 100-foot promontory overlooking Omaha Beach, with nothing more than ropes and rickety ladders. As enemy gunfire and grenades rained down, picking them off as they climbed, the Rangers secured the strategic high ground and silence a small battery of long-range German guns that had been moved inland.

The battle for Pointe du Hoc became of one the most heroic moments of the D-Day invasion. It was lionized by the legendary Hollywood film “The Longest Day” and by President Ronald Reagan, who stood on this hallowed ground to deliver one of his most famous speeches, extolling the bravery of the “Boys of Pointe du Hoc” on the 40th anniversary of the largest amphibious assault in the world's history.

But a little more than 3 miles down the windswept Normandy coastline, an archaeological dig on a vast swath of farmland is starting to tell another story about what took place that day. A World War II artefact collector and historian accidentally stumbled upon a massive German artillery installation that was buried after the invasion. His discovery, along with a trove of declassified U.S. and British military documents, threatens to alter the narrative of Pointe du Hoc and its importance as a military objective during the D-Day invasion.

Only now are historians beginning to reckon with the implications. Depending on which is talking, the discovery of what is known as Maisy Battery either calls into question the wisdom of the entire Pointe du Hoc operation or is simply one more footnote in a war full of footnotes.

One thing is certain: The mythology of Pointe du Hoc is firmly established. Those who challenge the story do so at their own peril.

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“Historians always shatter the idol, but let me tell you, when they do, they get a lot of pushback and angry emails in the middle of the night,” said Rob Citino, the senior historian at the National World War II Museum in New Orleans who has written 10 books about the war and only recently learned about Maisy Battery. “Pointe du Hoc is such sacred ground, it's like bringing someone to Gettysburg and saying, 'Actually, there was a much bigger battle fought just a few miles away.' ”

The artefact collector and historian Gary Sterne has received nothing but pushback since he found a map at a military flea market 15 years ago that led him to the discovery of Maisy Battery, a complex that covers 144 acres 1 mile inland between Omaha and Utah beaches - the prime objectives of the U.S. invasion forces. He has published a two-volume, 1,160-page encyclopaedia full of photographs, military documents and interviews with Army Rangers who climbed the cliffs of Pointe du Hoc.

His startling conclusion: The assault was unnecessary; the commander of the U.S. Army Ranger unit failed to follow orders, putting his men directly in harm's way; and U.S. military leaders should have targeted Maisy and its battery of heavy artillery guns instead of Pointe du Hoc, which the Germans had largely abandoned by the time of the Normandy invasion.

“I have nothing but respect for the Rangers and what they did at Pointe du Hoc,” Sterne said in a recent interview from his home in England. “It was truly heroic. But the facts are the facts.”

Sterne has been collecting military memorabilia since he was child growing up near Manchester, England. It became a full-time pursuit after he purchased a home in Normandy. In 2004, he travelled to Louisville, Kentucky, to attend one of the largest military flea markets in the world.

Beneath one of the 5,000 tables set up there, Sterne spotted a cardboard box. Inside was the complete uniform of a U.S. Army soldier who had fought in the Second World War. Sterne bought it for $180. Inside one of the pockets was a map of Normandy. The map was marked with hand-drawn circles, each with an “X” in the middle, and the words: “Areas of High Resistance.”

Sterne was confused. He knew the precise locations of those areas.

“I thought, 'There's nothing there. It's just fields,' ” Sterne recalled.

Back in Normandy, Sterne drove to the fields and started to walk through the tall grass. He came across a clearing and a large slab of concrete. At first he thought he had found the foundation of a building destroyed long ago. As he stepped off the slab, he tripped over a small chimney protruding from the concrete.

He was standing on the roof of a building, not the floor.

I have nothing but respect for the Rangers and what they did at Pointe du Hoc. It was truly heroic. But the facts are the facts Gary Sterne

“I thought, hang on a minute,” Sterne said. “It was a lightbulb moment.”

Sterne and his brother grabbed some shovels and began to dig. They unearthed a perfectly preserved, bombproof German ammunition bunker. He and his son, Dan, have been digging ever since, uncovering bunkers and barracks and large concrete gun placements. They discovered a field hospital, a command and control centre, evidence that an SS squad was embedded at the battery and the skeleton of a German soldier. All of it was buried by Allied forces after the invasion and Maisy was lost to history.

For nearly two years, Sterne kept his discovery a secret as he purchased dozens of tracts of land from their owners, quietly piecing together vast sections of Maisy for a World War II museum. When he went public with his findings in 2006 and opened the site to the public a year later, he said the backlash was ferocious. Other historians labelled him an opportunist, a fabulist, a “Mad Englishman.”

Sterne returned fire. He argued that Maisy, not Pointe du Hoc, should have been a primary target on D-Day. The guns at Maisy, he noted, were still firing three days after the invasion and capable of striking positions on Utah Beach, about 5 miles away. What he said next amounted to heresy in the military world.

Based on previously secret intelligence and field reports he obtained from military archives in the United States and Britain, Sterne said the Second Ranger Battalion commander of the Pointe du Hoc mission, Lt. Col James Rudder, knew that the Germans had removed their guns from Pointe du Hoc as the D-Day invasion neared. When Rudder and his men reached the top of Pointe du Hoc on June 6, 1944, the guns were gone, some of them replaced with long wooden telephone poles resembling artillery cannons. The real guns had been moved inland. The Rangers found five guns that had been moved from Pointe du Hoc that morning and disabled them with thermite grenades.

Sterne went further. He said Rudder jeopardized the lives of his men by disobeying orders. The declassified orders show that the Second Ranger Battalion was tasked with attacking Pointe du Hoc, moving inland and knocking out the German artillery batteries at Grandcamp and Maisy. The orders, issued March 26, 1944, directed Rudder's Rangers to “capture enemy batteries at GRANDCAMP and MAISY” after taking Pointe du Hoc.

Point du Hoc is on the Normandy Coast, overlooking the English Channel. US army rangers landed on the beach below on D-Day and scaled the cliffs using ropes and ladders (Scott Higham for The Washington Post)

Instead, Rudder attacked Pointe du Hoc, despite the reports documenting that the guns were being moved, and he remained in the area without advancing to Maisy. He later said he was ordered to hold the Grandcamp-Vierville Highway to prevent a German counter-attack. But Sterne said he could find no orders in the thousands of records he has reviewed directing Rudder to remain at Pointe du Hoc and hold that highway. Of the Rangers who served under Rudder during the invasion, 77 were killed, 152 were wounded and 38 were listed as missing in action.

Rudder, who died in 1970, went on to become a war hero, receiving the Distinguished Service Cross, and was later appointed president of Texas A&M University. One of the Rangers who said he fought under Rudder, Lt. George Klein, went on to become a world-famous narrator of the Pointe du Hoc story.

Klein frequently lectured about the assault, telling audiences that he was wounded by a German bayonet and had to be evacuated. During the 73rd anniversary of the invasion, Klein travelled to Normandy, where he was feted as “one of the great celebrities of the battle.” He signed autographs. He posed for pictures. He planted trees in Normandy villages.

But there was a problem: Klein never fought at Pointe du Hoc.

Instead of people looking at this dispassionately, it becomes a political hot potato Adrian Ridley-Jones, Normandy battlefield guide

Sterne said Klein visited Maisy during one summer and told Sterne that “you have your history all wrong.” Sterne had written a book by then called “Cover Up at Omaha Beach.” It was a based on interviews Sterne had conducted with Rangers who fought at Pointe du Hoc.

Sterne said he asked Klein about the role he played that day. Klein told him he had destroyed a gun pit at Pointe du Hoc. But records show that the gun pit had been destroyed months earlier. Klein said he was a lieutenant in F Company of the Second Ranger Battalion. But F Company already had a full complement of lieutenants. Klein could not recall details of the battle. The Rangers Sterne had interviewed could never forget. Klein said he returned to his original artillery unit after he was wounded.

Sterne and other historians found the papers documenting the activities of that artillery unit during D-Day. Klein and his unit were in Ireland on June 6, 1944.

Klein eventually admitted that he had fabricated his military past and the tales he told about the attack. The story was picked up by news outlets around the world.

Klein, like Maisy, faded into history. Now 98 and living in Illinois, he did not return calls for comment.

Each year, nearly 1 million tourists descend upon Normandy, many of them from the United States. Tour guides escort them to Omaha and Utah beaches, the American Cemetery and historic military sites, such as the town of Sainte-Mere-Eglise.

The piece de resistance of any tour is Pointe du Hoc.

Adrian Ridley-Jones, 63, a top-rated battlefield guide in Normandy, has recently added a new site to his tour: Maisy Battery.

The former signal officer in the British Army said he has come to appreciate the significance of the Maisy discovery and the documents Sterne has obtained. It has become increasingly clear to him that as D-Day approached, the need to take Pointe du Hoc diminished. The guns were gone, the Germans were changing their positions and the Pointe du Hoc mission would be perilous. He wonders why Rudder didn't alert his commanders that the guns were being removed from Pointe du Hoc and didn't urge them to make Maisy and Grandcamp the primary targets instead. Rudder never told his men that the guns had been removed, either.

“As archaeological evidence becomes clearer, history gets rewritten,” Ridley-Jones said. “Problems come as you do this. You upset preconceived ideas and entrenched positions. Instead of people looking at this dispassionately, it becomes a political hot potato.”

Ridley-Jones is careful to note the bravery of the Rangers at Pointe du Hoc.

“If it wasn't for the Americans, we wouldn't have won the war,” he said. “It was indeed a symbiotic relationship, and I am in no way denigrating them. ”

World War II historians note that the Germans built numerous batteries along the coast as part of Hitler's Atlantic Wall. Even though there were reports that the guns at Pointe du Hoc were being moved, the promontory remained a strategic position, occupying the high ground above Omaha Beach, where the Americans suffered their heaviest losses of the landing. A plan the size of the D-Day invasion, code-named “Operation Overlord,” is not easily changed.

“The fog of war was never foggier than on the morning of June 6, 1944,” said Rick Atkinson, a Pulitzer Prize-winning author who has written a three-volume history of the Second World War. “What is the overall impact on Operation Overlord and the specific events on the morning of June 6, 1944? Pretty minimal. There were a lot of moving parts; some of them were moving, and some of them were moving sideways. Did it cause substantial degradation of the operation? I don't think so.”

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Citino, the senior historian at the World War II museum in New Orleans, has been lecturing about Pointe du Hoc for 35 years. It's a story that captures the imagination of everyone who hears it.

“What you have at Maisy is little harder to explain,” Citino said. “It's interesting, and it's wonderful to see the outlines of a military base, but you can't take a little kid there and say, 'Look, Johnny, the Rangers scaled those cliffs with nothing but rope.' ”

Citino acknowledged that Maisy was an important installation for the Germans during D-Day, and U.S. military commanders might have considered placing it higher on their list of targets. The discovery, he said, is starting to change the narrative of what happened 75 years ago.

But changing history takes time.

“We are learning all the time and that's the best thing about the Maisy battery story,” Citino said. “Just below the surface, there are any number of buried stories that will tantalize us just as much as the Maisy Battery story. It clearly played a role in D-Day, and I never heard about it until five years ago. And I've been studying this all my life.”