A D-Day in military terminology is representative of the day that an attack is to be initiated, or the day that will mark the start of an operation. Those in the United States and those across the world know D-Day as the first day of the Invasion in Normandy on Tuesday June 6 of 1944, during World War II. The operation was named Operation Neptune, and turned out to be the largest water to land invasion in the history of the world. D-day was an effort committed by British, and American forces together against German Forces who were already in place on the beaches, prepared for battle. This famous first day of Operation Neptune is famously known for its large amount of casualties for both sides, and for being a turning point in World War II for the Americanâs and British. D-day was recently made popular by the movie âSaving Private Ryanâ which showed a firsthand account of how gruesome that this battle was.