The significant event that took place on D-Day during World War II was the Allied invasion of Normandy on June 6, 1944. This operation, known as Operation Overlord, marked a crucial turning point in the war, as it led to the liberation of Western Europe from Nazi occupation. American, British, Canadian, and other Allied forces launched a massive amphibious assault on five beachheads: Utah, Omaha, Gold, Juno, and Sword. The invasion involved meticulous planning and faced heavy resistance, resulting in substantial casualties. However, D-Day ultimately established a foothold in France, enabling the Allies to advance further into Europe and defeat Nazi Germany.