The Disappearing Spoon podcast

Topsy-Turvy Tales from Our Scientific Past
May 14, 2024 People & Politics

The Science of D-Day

To mark the 80th anniversary of the Normandy landings during WWII, we look at the surprisingly important role science played.

Photo for the invasion of Normandy on D-Day

This year is the 80th anniversary of the landing of the D-Day invasion. The military operation was a huge turning point in World War II and eventually helped the Allied Forces win the war. Science had a huge impact in the planning and execution of the mission. 

About The Disappearing Spoon

Hosted by New York Times best-selling author Sam Kean, The Disappearing Spoon tells little-known stories from our scientific past—from the shocking way the smallpox vaccine was transported around the world to why we don’t have a birth control pill for men. These topsy-turvy science tales, some of which have never made it into history books, are surprisingly powerful and insightful.


Host: Sam Kean
Senior Producer: Mariel Carr
Producer: Rigoberto Hernandez
Associate Producer: Sarah Kaplan
Audio Engineering: Rowhome Productions


Imagine it’s December 31st, New Year’s Eve. Normally a time of joy and celebration. But this is 1943, in Nazi-occupied France. 

It’s near midnight, just off the northern coast. It’s moonless out and dark. The wind is whipping around. Nazi machine guns loom on the bluffs, overlooking the beach. 

Suddenly, though, two lone figures emerge from the icy water. They’re exhausted from swimming in, but they don’t rest. They immediately get to work. They take depth readings in the water. Then they examine the beach.

They rub the soil and sand between their fingers and slip samples into baggies to take home—if they get home. At any moment, huge klieg lights could expose them, and send a hellfire of bullets tearing into their bodies.

So who was this daring duo? Intrepid spies? Special-ops commandos? Nope. They were geologists. Rock nerds who’d spent far more hours chipping stones than shooting guns.

As for what on Earth geologists were doing invading Nazi France, the answer is simple. They were doing geology. They were on a special mission to scout the beaches of France in preparation for June 6th, 1944. D-Day.

This summer marks the 80th anniversary of that invasion. And while you’ve probably never given much thought to the science of D-Day, several branches of science played vital roles. In fact, without the scientists, D-Day almost certainly would have been a fiasco—and might even have swung the entire war in favor of the Third Reich.

World War I was a war of trenches. So it makes sense that geologists were important then, to determine where best to dig. But World War II was a mobile war, dominated by tanks and trucks and airplanes. What does geology have to do with that?

More than you might think. To invade France, the Allies needed to land all their heavy vehicles on the beaches and drive them inland. Which meant they had to choose the landing sites carefully. Trucks and tanks don’t do much good if they’re stuck in muck. 

To this end, the Allies sponsored several clandestine geological raids on the French coast, to determine which beaches were suitable and which ones were not. The New Year’s Eve mission was one such raid.

These geological commandos would approach the coast at night in inflatable rafts or midget submarines. They often swam the last few miles to shore. Under the cover of darkness, they’d survey the beach and grab soil samples for analysis back in the labs.

They also measured the water depth, and mapped the speed and strength of currents. Then, after a full night’s work, they would plunge into the surf again and swim several more miles back to the raft or sub.

Overall, these geologists did incredible work. They combined the stealth and danger of undercover ops with the rigor of scientific research.

But they did commit one memorable gaffe. Geologists often use large screws called augers to take soil samples. On one raid, the geologists left an auger behind where the Nazis seemed likely to find it. Its presence on the beach could have betrayed where the upcoming D-Day invasion would take place.

As a result, Allied commanders seriously debated rounding up every auger in the free world; loading them onto planes; and carpet-bombing the beaches of France, to throw the Nazis off. Sadly, the auger bombardment never took place, due to wartime tool shortages. But the fear was real.

In addition to gathering data firsthand, geologists studied reconnaissance photos. Allied planes had been bombing the coasts of France for years. And geologists realized that the shape of bomb craters revealed a lot about the underlying soil.

It’s best to drive trucks and tanks on strong, cohesive soil. And strong, cohesive soil produced U-shaped craters when bombed. These craters had steep interior sides and there were large, solid chunks of material surrounding them. 

In contrast, you don’t want to drive tanks or trucks on weak or mucky soil. And weak or mucky soil produced V-shaped craters. These had sloped sides, and there were mud splatters or tiny chunks surrounding them. 

By searching photographs for V- and U-shaped craters, geologists could tell where the best soil was.

Similarly, the Nazis often stole hay carts from French peasants to haul heavy equipment around. But this ended up biting the Germans in the derrière. That’s because the depth of the ruts that resulted also provided clues about how strong the underlying soil was.

Based on their research, geologists convinced Gen. Dwight Eisenhower and his staff to abandon their preferred D-Day invasion site. Eisenhower’s team had wanted to invade Brittany. But the geologists told them to focus on nearby Normandy, whose beaches offered better traction. 

Had Eisenhower not listened, D-Day would have gone very differently. Upon reaching shore, the Allies would have floundered, bogged down in soft soil. And while they struggled, the Germans would have swarmed them over the next few days, pummeling them on the beaches with bombs and machine guns. We would have blown D-Day!

Imagine the consequences. Without D-Day, it could have taken years longer to defeat Germany. The Nazis might even have wrestled the Allies into a stalemate. Heck, a rump Nazi state might still exist today. It’s a chilling thought.

As it was, the Allies landed nearly 9,000 heavy vehicles on D-Day, and 150,000 in the first seven weeks. Thanks to our geological prowess, D-Day was a smashing success.

But there was more to D-Day than just moving trucks and tanks. Because again, World War II was a war of the air. What did planes have to do with geology?

Well, planes aren’t permanently in the sky; they have to land sometimes. So the Allies needed airstrips. And they needed airstrips in France.

The Allies did have bases in southern England to send fighters over on D-Day. But fighter planes back then had very limited ranges. They could spend just a few minutes in the air across the English Channel before they had to fly back home.

And without planes defending them, the D-Day troops and vehicles in France would be sitting ducks for German planes. They’d be bombed to oblivion. So one top priority after landing on D-Day was to pave some airstrips, pronto.

Unfortunately, you can’t just build airstrips wherever. You need firm soil that drains well. So once again, it was geologists to the rescue. One geologist landed with the troops on D-Day, and several more were rushed over right after. They helped lay down twenty crucial airstrips over the next two months, mostly on a limestone formation from the Jurassic Age. 

Geologists also advised the Allies on where deposits of metal were. That’s because metallic ores can interfere with the metal detectors they used to sweep for mines. Geologists located groundwater for the troops to dig wells, too. Both were small but crucial aspects of the invasion.

To be sure, the soldiers who landed at Normandy deserve the lion’s share of the credit for D-Day. But the geologists put those troops in a place to succeed. One historian called those military geologists “the biggest bargain the [U.S.] Army has ever got in wartime.”

But even if the geology of D-Day had been perfect, another branch of science still could have screwed things up at the last minute. Meteorology. 

As much as we all love complaining about them, making weather forecasts is really, really hard. If you were to rank the most complex structures or systems known to exist in the universe, what do you think would be at the top? The human brain. But number two is probably the Earth’s atmosphere, and the weather it produces. Weather is really complicated.

So imagine you’re an army meteorologist in 1944. You have no computers, no satellites. And people already think weathermen like you are full of crap. Now Dwight Eisenhower himself comes to you with top-secret information.

The Allies are planning a huge assault next week on Normandy, D-Day. The outcome of the whole war hangs in the balance. So Eisenhower asks you. What day next week will have the best weather? 

Gulp. If you screw this up, and send the troops into foul weather, they’ll get slaughtered. And the element of surprise will be lost—you don’t get a redo on D-Day.

Thankfully, Eisenhower’s team did not screw things up. In fact, just like his geologists steered him away from landing in Brittany, the meteorologists pushed Eisenhower away from his preferred landing day on June 5th. They insisted that June 6th would have better weather. Eisenhower wisely listened, and things proceeded brilliantly.

Now, there are other scientific aspects of D-Day we could discuss. For instance, medicine. During the boat rides across the English Channel, the troops received some of the world’s first pills for seasickness. 

And although some soldiers felt a little drowsy after taking them, others reported that they worked great. These soldiers normally puked every time they stepped onboard a ship, but they suddenly found themselves fresh and peppy upon landing. And good thing. Imagine if they’d showed up green and wobbly, and tried to fight the Germans. It would have been ugly.

But of all the scientific angles of D-Day, one stands out the most to me—a field of science you probably wouldn’t think to connect to battle back then. Radioactive warfare.

My book The Bastard Brigade details the top-secret mission to stop the Nazi atomic bomb project. Many scientists on the American Manhattan Project were refugees from Nazi Germany. And they were terrified that the Germans were far ahead of us in atom-bomb research. They thought Adolf Hitler would soon possess the most powerful weapon in world history.

That fear also affected the planning for D-Day. Now, the Allies knew that the Nazis probably wouldn’t have a working atom bomb by then. But beyond atom bombs, radioactive elements can still kill people through so-called dirty bombs.

Atom bombs kill you by releasing gobs of energy all at once; they vaporize you. Dirty bombs kill by releasing atoms that bombard you with deadly radioactivity. They wriggle inside your body and poison you. 

And while atom bombs require a chain reaction and produce a mushroom cloud, dirty bombs do not. You simply have to spread the dirty radioactive material around. You can do that with regular explosives. You can even mix the radioactive material with smoke or powder and use crop-dusters to spray it around.

Dirty bombs are well-suited to resisting invasions. Even a few hours of exposure to radioactive elements will kill troops. And because radioactivity is invisible, soldiers might not realize they’re being poisoned until it’s too late. 

Equally bad, radioactive atoms are virtually impossible to scrub clean. So once they poison a parcel of land, the invading force cannot occupy the land for months, even years.

Plus, the Third Reich didn’t need to poison the entire landscape. They needed to poison only certain key areas: ports, bridges, railyards, airports, water reserves. By concentrating on key infrastructure, the Nazis could neuter the entire D-Day operation.

All of which terrified folks on the Manhattan Project. They first warned Allied commanders about radioactivity in April 1944. Now, Winston Churchill actually rolled his eyes at the Americans over this. He thought the whole thing sounded silly. 

But Dwight Eisenhower was spooked. He soon initiated what’s called Operation Peppermint. It was history’s first attempt to grapple with radioactive warfare.

For Operation Peppermint, several foot soldiers received training with Geiger counters. These counters were the size of lunchboxes. They were housed in grey, watertight cases, and they emitted a tone whenever they detected something. Troops planned to carry them into battle on D-Day. 

The initial plans for Peppermint called for eight four-man Geiger-counter teams spread among the invading D-Day forces. The number actually deployed remains unknown, although some did reportedly join the landing at Omaha Beach.

Medical personnel also played a role in Peppermint—albeit unknowingly. A few days before June 6th, field doctors received orders to keep an eye out for clusters of certain symptoms. Fatigue, nausea, rashes, low white-blood-cell counts.

Those are all signs of radioactivity poisoning. But to avoid spreading fear, the doctors never learned the reason for their vigilance. Their superiors made up a story instead about an outbreak of some exotic germs that needed tracking.

Another aspect of Operation Peppermint involved, of all things, dentistry. Again, the Allies trained a few soldiers to use Geiger counters. But Geiger counters were unreliable back then, prone to malfunctions. So the troops needed something more trustworthy to detect contamination. Someone suggested dental film, which is quite sensitive to radioactivity.

As a result, several units among the D-Day forces were handed rolls of film before the invasion. They also had orders to stop every so often—in the field—to develop the film.

And again, these troops weren’t told why they were doing this. The cover story was that a few crates of expensive film had been ruined recently, and the higher-ups wanted to nail down the cause.

Now, this must have seemed like sheer raving lunacy. Imagine the chaos of D-Day—troops storming the beaches, dogfights in the air, angry Nazis strafing you with gunfire. And now you’ve got orders to stop and develop some dental film? What on Earth?!

But, the soldiers no doubt chalked it up to the Catch-22–like madness of the army, and did as they were told. However crazy it seemed, their efforts removed a weight from the minds of Allied leaders and allowed the D-Day operation to proceed without fear.

By the by, the Allies weren’t the only ones throwing all the science they could at the war. Nazis scientists actually invaded North America and set up a secret weather station in Canada. It was part of what’s called the Weather Wars.

I’ve actually written a bonus episode about the Nazi Weather Wars at The bonus also includes details on the very last Nazis to surrender—on another secret station in the arctic, several months after the Third Reich’s demise. It’s a bizarre tale. Check it out at

So, there you have it—the science of D-Day. And even though the invasion took place 80 years ago, in some ways, the story is still being written.

Recently, a few geologists studied the sands of the Omaha Beach landing site. And they noticed something curious mixed in with the sand—microscopic spheres of iron and glass. The glass comes from sand crystals that melted and fused from the incredible heat of bombs dropped on D-Day. The iron comes from bomb shrapnel, or from vehicles that got blown up and were abandoned.

In the 80 years since, the shrapnel and vehicle remains have been slowly decomposing, adding brand new components to the sand. In other words, D-Day actually changed the geology of the beach. Those little bits of iron and glass are now a permanent part of the story of the most consequential day, scientifically and otherwise, of the twentieth century.

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