The significant military campaign that marked the arrival of the Allied forces on D-Day was Operation Overlord, launched on June 6, 1944. This operation involved a massive amphibious invasion on the beaches of Normandy, France, and represented a turning point in World War II. Approximately 156,000 Allied troops landed on five beachheads, facing fierce resistance from German forces. The successful landings allowed the Allies to establish a crucial foothold in Europe, ultimately leading to the liberation of occupied territories and contributing to the defeat of Nazi Germany in subsequent months.