“Operation Neptune” was the codename for the Normandy landings that were carried out on Tuesday, June 6th, 1944 – aka D-Day. It was the largest seaborne invasion in history. The plan for the invasion took into account the phase of the moon and the tides, so, although the weather was far from ideal, it was either carry it out on June 6th or wait two weeks for similar lunar/tidal conditions. The idea was that the full moon would provide light for the aircraft pilots, and there would be the highest tides.
The Normandy coast was divided into five sections: Utah, Omaha, Gold, Juno, and Sword. When the armies reached the beaches, they encountered heavy gunfire, not to mention that the shores were covered with wooden stakes, metal tripods, and barbed wire. Omaha beach saw the largest number of casualties.
The Allies had intended on overtaking Carentan, St. Lô, Bayeux, and Caen on the first day – this did not happen. The five beaches were not connected until June 12th.
Operation Neptune is credited as the beginning of the liberation of German-occupied northwestern Europe.
Part 1

From Jeff’s Youtube description:
“Universal Newsreel, in full co-operation with the War Department, presents official pictures of the final military preparations for the launching of D-Day. A host of nations engage in the huge task. The invasion, in truth, is a United Nation’s effort.”

Part 2