They weren’t terribly accurate, but they did provide some information which would be useful to mariners and to citizens. And so, even in the mid-1700s in colonial America there were tide predictions of the timing of the tides at various harbors. The tide is related to the position of the sun and the moon relative to the Earth, and so going back even to the mid-1700s, people understood that when you had high tide every day, and how high the tide was, relates to, in particular, the phase of the moon. GREG DUSEK: “Tide predictions enable us to tell when is high and low tide and what time is high and low tide going to occur at different coastal locations. Today, tide predictions are made on electronic computers. It was the first machine made to simultaneously compute the height of the tide and the times of high and low waters.
2, fondly referred to as "Old Brass Brains," to predict tides from 1912-1965. Coast and Geodetic Survey used tide prediction machine No. Can you tell us a bit about the basics of what tides are and how people predicted tides in the past, leading up to WWII? HOST: And this was of course well before computers.
So all of the work done relating to tide predictions was really secretive and it was a lot of work to make sure that none of that information escaped and was available to the enemy.” And then the other important part was that, if we were generating predictions for positions we were likely to attack, if the enemy found those predictions, it might tip them off as to where we were thinking about attacking next. GREG DUSEK: “So tide predictions were top secret during WWII, and the reason for that was you wanted to limit the axis information about allied-held coasts, you didn’t want to divulge any information that they might not already have about the tide or our own coastlines, so they couldn’t plan their own attacks. That last part, looking for a time with low tide shortly after dawn, is where we get to the science of predicting the tide for a particular location. HOST: That is a lot of environmental factors to have all fall into place. Those criteria, you know, didn’t have a lot of times to work with, and June 5th, 6th, and 7th of 1944 were the three days that were identified.” And the reason they needed it shortly after dawn, was because they needed a couple hours of time for the amphibious assault groups to travel across the English Channel in darkness, but then enable the Naval bombardment to have daylight to be able to target initial areas of interest to bombard, before the amphibious assault began. And then, lastly, they were looking for a time with low tide shortly after dawn.
So they wanted close to a full moon the night before. They also wanted to have a time period where you had a full moon or close to a full moon the night before the assault, and the reason for that was, they were going to have airborne infantry sent behind enemy lines the night before, and to do that, you needed some sort of lights for them to be able to figure out where they’re going.
But they knew that, in the summer months, you were more likely to have good weather, so they wanted to plan a time in the summer for the assault. Because they were going over the ocean, they needed good weather, so they needed to find a time where the waves were going to be minimal and the winds were going to be minimal, and obviously that’s something they really can’t plan ahead of time. They were going to cross the English Channel to the French coastline, near Normandy. GREG DUSEK: “So the allies were planning an amphibious assault. What sort of conditions were the allies looking for as they planned the invasion of Normandy? Greg, thanks for joining the NOAA Ocean Podcast. Joining us by phone today to tell us the story of D-Day from the perspective of the science of tides and tide predictions is Greg Dusek, a physical oceanographer and senior scientist at the Center for Operational Oceanographic Products and Services, or CO-OPS - the tides and currents office of the National Ocean Service. But most people don’t know how ocean tides played a crucial role in the initial phase of the invasion. All told, D-Day marked the start of the liberation of German-occupied France (and later western Europe) and laid the foundations of the Allied victory on the Western Front. It was a massive, complex amphibious landing along the Normandy coast of France that began on Jwithin ten days there were half a million troops ashore, and within three weeks there were two million. D-Day, codenamed Operation Neptune, was the largest seaborne invasion not only in World War II, but in history. HOST: This is the NOAA Ocean Podcast, I’m Troy Kitch.