Skip to main content

D Day

D DAY

D DAY. The term "D Day" indicates the beginning of an attack or other military operation when the specific date has yet to be selected or secrecy is required. "H Hour" is similarly used to designate the time of the attack.


The "D" and "H" are derived from the first letters of "day" and "hour." There is one D Day and H Hour for all units participating in an operation. Plus and minus signs are used to indicate the number of days or hours that precede or follow the specific operation. Thus, 舑5 means five days before D Day and H + 2 means two hours after H Hour.

Planning for operations can begin months before the anticipated time of the operation. The use of D Day minus "X number of days" signifies the date by which certain actions, such as planning or the training of units, must be complete. At the appropriate time an order is published giving a specific date for D Day.

The U.S. Army first used the term on 7 September 1918, when it issued First Army Field Order Number 9: "The First Army will attack at H Hour on D Day with the object of forcing the evacuation of the St. Mihiel Salient." The term is most commonly associated with the invasion of Normandy on 6 June 1944.

Frank R.Shirer

See alsoNormandy Invasion .

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"D Day." Dictionary of American History. . Encyclopedia.com. 18 Oct. 2017 <http://www.encyclopedia.com>.

"D Day." Dictionary of American History. . Encyclopedia.com. (October 18, 2017). http://www.encyclopedia.com/history/dictionaries-thesauruses-pictures-and-press-releases/d-day

"D Day." Dictionary of American History. . Retrieved October 18, 2017 from Encyclopedia.com: http://www.encyclopedia.com/history/dictionaries-thesauruses-pictures-and-press-releases/d-day

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.