what does the d in d day stand for

From the "Word IQ" site on the web:

"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."

More than you ever wanted to know, I'm sure.

Surely, you jest about the "'Nam" thing. (What ARE they teaching in today's schools? Never mind, I don't really want to know).

Are you really Radar? Do you hear me? Hello?