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In military parlance, D-Day is a term often used to denote the
day on which a combat attack or operation is to be initiated. By far the most well-known D-Day is June 6, 1944 - the day on which the Battle of Normandy began - commencing the liberation of mainland Europe from Nazi occupation during World War II. This article discusses the general use of the term D-Day. Refer to
the Battle of Normandy article for a description of the events
of June 1944.
The terms D-day and H-hour are used for the day and hour on which a combat attack or operation is to be initiated. They
designate the day and hour of the operation when the day and hour have not yet been determined, or where secrecy is essential.
The letters are derived from the words for which they stand, "D" for the day of the invasion and "H" for the hour operations
actually begin. There is but one D-day and one H-hour for all units participating in a given operation. It is unnecessary to
state that H-hour is on D-day.
When used in combination with figures, and plus or minus signs, these terms indicate the length of time preceding or following
a specific action. Thus, H-3 means 3 hours before H-hour, and D+3 means 3 days after D-day. H+75 minutes means H-hour plus 1 hour
and 15 minutes.
Planning papers for large-scale operations are made up in detail long before specific dates are set. Thus, orders are issued
for the various steps to be carried out on the D-day or H-hour minus or plus a certain number of days, hours, or minutes. At the
appropriate time, a subsequent order is issued that states the actual day and times.
The earliest use of these terms by the U.S. Army that the
Center of Military History has been able to find was during World War I. In
Field Order Number 9, First Army, American Expeditionary Forces, dated September 7, 1918: "The First Army will attack at H hour
on D day with the object of forcing the evacuation of the St. Mihiel Salient."
D-day for the invasion of Normandy was set for June 6, 1944, and that date has been popularly referred to by the short title
"D-day." (In French, it is called jour-J.)
Sources
- The General Service Schools, Fort Leavenworth, Kansas, Combat Orders (Fort Leavenworth, Kansas: The General Service
Schools Press, 1922).
External link
D-Day (short for Decimal or Decimalization Day, but also deliberately
evoking memories of the previous D-Day) was also used in Britain in 1971 to denote the day on which the British currency was
decimalized - February 15, 1971. See
Decimal Day for an account.
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