On D-Day, 6 June 1944, Allied forces launched a combined naval, air and land assault on Nazi-occupied France. The 'D' in D-Day stands simply for 'day' and the term was used to describe the first day of any large military operation.

Most argue it was merely a redundancy that also meant day,  but others have proposed everything from departure  to decision  to doomsday.  According to the U.S. military, D-Day  was an Army designation used to indicate the start date for specific field operations.