D-Day refers to June 6, 1944, when Allied forces launched a massive invasion of German-occupied France during World War II. This operation, known as Operation Overlord, involved over 156,000 troops landing on five beachheads in Normandy, including Omaha and Utah beaches. The invasion marked a significant turning point in the war, as it began the liberation of Western Europe from Nazi control. The planning for D-Day was extensive, involving deception strategies to mislead the Germans about the invasion's location and timing. The success of the operation relied on cooperation among Allied nations, including the United States, United Kingdom, and Canada. D-Day ultimately paved the way for the Allied advance into Germany and contributed to the eventual defeat of the Nazi regime.