<P> In the military, D - Day is the day on which a combat attack or operation is to be initiated . The best known D - Day is during World War II, on June 6, 1944--the day of the Normandy landings--initiating the Western Allied effort to liberate mainland Europe from Nazi Germany . However, many other invasions and operations had a designated D - Day, both before and after that operation . </P> <P> 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 . For a given operation, the same D - Day and H - Hour apply for all units participating in it . When used in combination with numbers, and plus or minus signs, these terms indicate the point 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 . (By extension, H + 75 minutes is used for 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 . </P> <P> Other days such as A-Day (Battle of Leyte), L - Day (Battle of Okinawa) etc. have different meanings for the military . </P>

Where does the name d day come from
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