The codename for the invasion of Normandy was Operation Overlord. It took place on June 6, 1944.

Operation Overlord was the largest amphibious assault in history, involving the landing of Allied forces on the beaches of Normandy, France during World War II. The objective of the operation was to establish a foothold in German-occupied Western Europe and ultimately liberate mainland Europe from Nazi control.

The invasion was meticulously planned and carried out by the Allied forces, under the overall command of General Dwight D. Eisenhower. The operation involved the coordination of land, air, and naval forces from multiple countries, including the United States, United Kingdom, Canada, and other Allied nations.

The D-Day landings, as they are commonly referred to, began early in the morning on June 6, 1944. The beaches of Normandy were divided into five sectors, each assigned to a different Allied force. These sectors were named Utah, Omaha, Gold, Juno, and Sword. Each sector had its own set of challenges and objectives.

For example, Omaha Beach, assigned to the American forces, proved to be the most heavily defended and challenging landing zone. The troops faced strong resistance from German defenders and suffered heavy casualties. However, through sheer determination and bravery, the Allied forces were able to secure the beachhead and push inland.

References:
History.com - D-Day
The National WWII Museum - D-Day: The Allied Invasion of Normandy

Overall, Operation Overlord, also known as the invasion of Normandy, played a crucial role in the eventual Allied victory in World War II. It marked a turning point in the war and paved the way for the liberation of Europe from Nazi occupation.