Today is the 70th anniversary of D-Day, the day Allied forces in WWII invaded Normandy.

It just occurred to me that I have nothing better than guesses for what the "D" actually stands for, and my initial searches turned up a number of reasonable guesses. ("Deployment," "Designated," etc.")

EDIT: It seems that the "D" is generally thought to refer to "day," so the obvious question is "Why call something D-Day if the the D simply makes it mean 'Day Day'"?

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    Well, I learnt something today, then. I’m one of the (apparently numerous) people who had been walking around with a false folk etymology (debarkation or disembarkation in my case) all these years. I could have found that out in about 30 seconds by doing a Google or dictionary search, though, which makes this question off-topic as General Reference. – Janus Bahs Jacquet Jun 6 '14 at 17:28
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    @Fumble I don’t think GR has to be common knowledge for native speakers. “What does cataphatic mean?” would be a question the answer to which I doubt would be common knowledge for most native English speakers; but the word is clearly described in any decent dictionary, so it’s still GR. – Janus Bahs Jacquet Jun 6 '14 at 17:36
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    @medica: I usually closevote on the basis that the question isn't of interest to linguists, etymologists, and (serious) English language enthusiasts. And (perhaps uncharitably) I don't usually classify people with highly limited command of English as "serious enthusiasts". – FumbleFingers Jun 6 '14 at 17:51
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    I'm struggling a little with the notion that this is "general reference" despite multiple folks here indicating not knowing the answer, and actually having assumed seemingly incorrect ones. But, in the interest of improving it, I edited to incorporate why such a term would be introduced, given that it seems entirely redundant. – Jaydles Jun 6 '14 at 18:12
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    I support leaving this question open. – Kit Z. Fox Jun 6 '14 at 18:47

The key to understanding "D-Day" is in how other days in the operation are referenced. The "D" does refer to "day", and in planning a complex operation, certain things have to happen on or by earlier dates; these are scheduled as, say, "D-7" for seven days before the op.

These relative date references are more useful than absolute dates for two reasons: one, you don't have to rewrite the whole plan if the target date changes, and two, you can keep the target date secret while discussing logistics with a lot of subordinates.

So all the other days in the op are "D minus 7" or "D plus 3". The target date is "the day we're calling D", or "D-Day."

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    Similarly, T minus 2 hours from shuttle launches. – Bobson Jun 6 '14 at 19:30
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    Yep, though secrecy has been less important in the U.S. space program. :) In space launch sequencing, it's also common for the clock to get started and stopped prior to launch -- more than one hour might elapse between T minus 2 hours and T minus 1 hour. I believe after launch the clock isn't ever stopped, though. – Russell Borogove Jun 6 '14 at 20:37

According to the U.S. Army (here) it simply means "Day". "H-Hour" is also used, with the "H" meaning "Hour". I'm not quite sure why the redundancy exists; but that's how it goes, I guess.

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    It is to emphasize the big day from any other day in discussions. Since the actual date is decided late, they need a proper name for it before that. – Oldcat Jun 6 '14 at 18:04
  • They could call it "T-Day", or just "The Big Day" :-) – Matt Gutting Jun 6 '14 at 18:13
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    They could call it 'Norman', but they decided not to. – Oldcat Jun 6 '14 at 18:15
  • I could actually see them calling it "Day D" or "Hour H", along the lines of "Brand X". I'm not sure why they would have reversed the pattern, though. – Matt Gutting Jun 6 '14 at 18:19
  • Because it is a day, not a D. – Oldcat Jun 6 '14 at 18:20

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 June 6, 1944 — the day of the Normandy landings — initiating the Western Allied effort to liberate mainland Europe from Nazi occupation during World War II.

Basically H−8 means 8 hours before H-Hour, and D+7 means 7 days after D-Day.By extension, H+80 minutes is used for H-Hour plus 1 hour and 20 minutes.

So D in D-Day stands for Designated

Read these pages: http://en.wikipedia.org/wiki/Military_designation_of_days_and_hours


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    From your own Wiki link: "Contrary to popular belief, the "D" does not stand for any specific word – the most popular being disembark. (NATO). According to history.army.mil/faq/ddaydef.htm the "D" stands for "Day"." The rest of your answers sounds good. P.S. That down-vote was not mine. – Cerberus_Reinstate_Monica Jun 6 '14 at 17:27
  • Ummm, must read more about this now :D Thank you @Cerberus :) – gkmohit Jun 6 '14 at 17:28
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    I don't see how you got from your first two paragraphs to So D in D-Day stands for Designated. – Bobson Jun 6 '14 at 19:58
  • Not sure that's correct, in France it was referred to as J-Jour which fits with the D (or J) standing for day (or jour) as indicated by the other responses. – Joe Fawcett Jun 17 '14 at 16:06

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