Why was it called D-Day?

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Contrary to popular mythology, the D in D-Day has nothing to do with Doomsday or Deliverance Day. Nor does the D stand for 'disembarkation' or 'debarkation'. If it stands for anything at all, it is 'day'. This is because D-Day, in military terminology, is simply the day on which an operation is planned to begin.

The D-Day Museum at Portsmouth explains:

'When a military operation is being planned, its actual date and time is not always known exactly. The term "D-Day" was therefore used to mean the date on which operations would begin, whenever that was to be. The day before D-Day was known as "D-1", while the day after D-Day was "D+1", and so on. This meant that if the projected date of an operation changed, all the dates in the plan did not also need to be changed. This actually happened in the case of the Normandy Landings. D-Day in Normandy was originally intended to be on 5 June 1944, but at the last minute bad weather delayed it until the following day. The armed forces also used the expression "H-Hour" for the time during the day at which operations were to begin.'

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