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Why the science of tides was crucial for D-Day

P A Thompson
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June 6, 1944 the Allied forces stormed the beaches of Normandy and took the Nazis by surprise in the largest sea-to-land invasion in history.

This would be remembered as D-Day. It ultimately led to the end of World War II in Europe. However, this planned attack wouldn't have been possible without deep, specific knowledge of ocean tides.

"If you got that wrong, you could have had all of your landing craft stranded on the beach and potentially completely messed up the D-Day invasion," says Gregory Dusek, a senior scientist with the National Oceanic and Atmospheric Association.

Earthly tides have a lot to do with celestial bodies beyond our planet. They're contingent upon the sun, the moon and earth gravitationally pulling on each other.

One way to visualize this is to think Earth being entirely covered in water — like being engulfed in a giant water droplet. When the sun and the moon pull on this huge droplet, the water bulges where those gravitational pulls are strongest. As Dusek explains, "If I'm standing on this water covered Earth at a point somewhere, the Earth is rotating underneath this water. And so as I pass one of these bulges, I'm experiencing a high tide. And then as I get past it, I experience a low tide."

But the connection between the tides and the moon goes deeper.

The tides also vary according to the phase of the moon. When there is a full or new moon the tides are at their most extreme.

Humans have long been aware of these changes to the ocean. People have been charting tides for over a thousand years — and discussing them for thousands of years longer.

In modern times, understanding tides not only helps win battles, it also affects how we ship goods globally and where we build homes. That's why NOAA has put out a report capable of predicting coastal flooding up to a year in advance. Scientist also hope to harness tides as a green energy source. Underwater turbines can generate power when strategically positioned in areas with strong tides like the Bay of Fundy.

Want to hear us cover more science history? Email us at shortwave@npr.org.

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This episode was produced by Rachel Carlson and Hannah Chin, edited by Rebecca Ramirez. Rebecca checked the facts alongside Rachel. Robert Rodriguez was the audio engineer.

Copyright 2024 NPR

Regina G. Barber
Regina G. Barber is Short Wave's Scientist in Residence. She contributes original reporting on STEM and guest hosts the show.
Rachel Carlson
Rachel Carlson (she/her) is a production assistant at Short Wave, NPR's science podcast. She gets to do a bit of everything: researching, sourcing, writing, fact-checking and cutting episodes.
Hannah Chin
Rebecca Ramirez
Rebecca Ramirez (she/her) is the founding producer of NPR's daily science podcast, Short Wave. It's a meditation in how to be a Swiss Army Knife, in that it involves a little of everything — background research, finding and booking sources, interviewing guests, writing, cutting the tape, editing, scoring ... you get the idea.
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