It's 6th June 1944, in Normandy, France. The Allied troops prepare the largest amphibious operation in history, against Nazi Germany. D-Day has come. While the infantry and armoured divisions wait for the green light, the weather charts are constantly updated.
A recently declassified dossier shows that swell, surf height and wind were crucial variables taken in consideration in the Operation Neptune. It involved tides, winds, waves, visibility both from the air and the sea stand-point, and the combined employment of land, air and sea forces in the highest degree of intimacy and in contact with conditions that could not and cannot be fully foreseen.
On the 1st February, the British Admiralty's Naval Meteorological Service activated a Swell Forecast Section in order to get accurate wave predictions for D-Day, the Big Storm (19th-22nd June 1944) and over-the-beach supply operations following the destruction of the artificial harbor at the Omaha beachhead.
Two years before the Operation Overlord (Normandy landings) and Operation Neptune, Franklyn Roosevelt, the US President at the time, sent a message to Winston Churchill, the British Prime Minister, showing his concern. "...bad surf on the Atlantic beaches is a calculated risk."
Nearly one million equipped troops were extremely sensitive to wave action. It would not be easy to deploy everyone and everything, quickly and efficiently. The report from Charles C. Bates, retired Lieutenant Colonel of the U.S. Air Force tells "it needed a four-day period of low seas".
Studying the conditions of the oceans was crucial. Back then, waves meant casualties, not pleasure. That's why it was decided that the Royal Naval Meteorological Service would have the sole responsibility in generating the sea, swell and surf forecasts for strategic decision taking.
Graphs for relating wave height and period to wind speed and associated fetch and duration, as well as an estimate of their decay rate were created. Knowledge was power.
Additionally, wave forecasters of the Allied force received top secret aerial photographs of what the surf zones were like at the designated beachheads, in order to complement their information and prediction. ""Notes on the Sea, Swell, and Surf in the English Channel" is the first confidential report issued by the surf forecast team.
A 6-way conference call was established to get updates on the condition of the waves. The day of the attack was going to depend on the surf conditions. The staff of meteorologists included Donald Yates (Colonel, USAF), James Stagg (Group Captain, RAF) and John Fleming (Instructor Commander, RN).
Tension builds on the 3rd June 1944. Eisenhower demands morning and evening swell updates. The D-Day was coming. On the 4th June, the forecast for next 48 hours had 2-4 foot wind waves for the assault areas.
What was considered "The Most Important Weather Forecast in the History of the World" came on Monday, 5 June 1944, at 0400 DBST. "Okay! Let's go!", said Dwight Eisenhower. The observed wave conditions at Operation Neptune's beachheads on the 6th June were: 2-6 foot waves with "choppiness [that] makes personnel transfer difficult."
Although the Swell Forecast Section's wave forecasting models became quickly outmoded post-war, it is widely accepted their enormous contribution to the science of predicting swells and surf. The Allies of World War II won and the planet was free of Nazi domination.
Read "Surf Forecasting For Invasions During World War II". Learn more about how waves are formed.