The armed forces use the term D-day to designate when a military operation 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, most of them landings on enemy-held coasts, it was the June 1944, invasion of Normandy (photo, above) that was remembered in history as the D-day. It constituted the largest seaborne invasion in history. After several delays due to poor weather, the Allied troops crossed the English Channel and arrived on the beaches of Normandy on the morning of June 6. Brutal fighting ensued that day, with heavy losses on the both sides. At the end of the day, the Allied troops had taken hold of the beaches — a firm foothold that would allow them to march inland against the Nazis, eventually pushing them back to Germany. While it was a critical Allied victory, the invasion on Normandy was still to be followed by 11 more months of bloody conflict: Germany did not surrender until May 7 of the following year.