The military uses the term D day to designate when an initiative is set to begin, counting all events out from that date for planning. For example, “D day minus two” would be a plan for what needs to happen two days before the beginning of the military operation. While the military planned and executed many D days during World War II (1939–45), most of them landings on enemy-held coasts, it was the June 6, 1944, invasion of Normandy that went down in history as the D Day.