D-Day's D Simply Meant Day

The "D" in D-Day simply meant "day." Military planners used D-day for the date an attack or operation would begin and H-hour for its starting time, particularly when the exact schedule remained secret or undecided. This allowed other events to be scheduled as D-1, D+1, H-3, and so on, although the Normandy invasion made D-Day synonymous with June 6, 1944.

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