The significance of the D-Day invasion, which took place on June 6, 1944, was its role in establishing a major Allied foothold in Europe during World War II. Known as Operation Overlord, the invasion involved the largest amphibious assault in history, with Allied forces landing on the beaches of Normandy, France. This decisive operation marked the beginning of the liberation of Western Europe from Nazi occupation. The success of D-Day significantly weakened German forces and paved the way for further Allied advances. D-Day is memorialized as a turning point in the war, demonstrating the effectiveness of Allied cooperation and strategic planning.