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 which 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".