in D-Day

What does the 'D' stand for in D-Day? I have heard at least a couple of inconsistent explanations and would like to know the truth.

Paul J.

D Stands the the Day in which the operation will take place and H is the Hour it will take place.

We are talking military planners' jargon here.

Operations are generally planned for a target date but must allow for that date to be brought forward or pushed backward by external factors.

Hence, the planners use a shorthand in which days before the start of an operation are known as ... D-5, D-4, D-3, D-1 and days after the start of the operation are D+1, D+2, D+3, D+4, D+5 ...

As you can see, the examples above leave out the day of the start of the operation itself. You could call it D-0 or D+0 - same thing - but by convention it is known as D-Day. This is, of course, an oxymoron as in full it would be 'Day-Day'

In operations requirng detailed planning you can have H-Hour and theoretically M-Minute or even S-Second!

Today we tend to think of 'D-Day' as synonymous with 6th June 1944 but most if not all major allied operations would have had its own D-Day. If you read, for example, about operations Goodwood and Epsom, themselves not long after 6th June, you will get very confused (as I did) until you realise this point.

I don't know if this planners' jargon is British or American in origin, but I suspect the former. It would be interesting to learn what nomenclature was used in the PTO. That would give us a clue. Anybody?

HTH Herb

D-Day? I have heard at least a couple

The D simply stands for the particular day an operation begins, typically an invasion. H hour is the same thing it stands for the hour that an operation begins.

The point is that people can refer to D day and H hour without revealing the actual day or hour or indeed without even knowing those facts.

There is a Defense Department web site that gives formal definitions of D day and H hour.

You're probably going to get a dozen answers to this all saying more or less the same thing, but here goes anyway. It stands for 'day'. It's another way of saying The Big Day. There were actually many D-Days all through the war as that was the usual way of designating the day that an operation was set to begin. History has for a variety of reasons pick this one out for special notice.

You might also confer 'H-Hour'.

As the military staffs draw up planning documents for all major operations, you have to deal with many specifics that are unknown. You write the documents, as much as you can anyway. Both for flexibility, and security, dates and times are the last things to be filled in.

So for many plans, the month is just left as 'M-Month' the day is written as 'D-Day' the hour is recorded as 'H-Hour' the minute is 'M-Minute' *

The Normandy Invasion, was just one of many 'D-Days' but as it is very famous, and important, and high in memory and publicity, the name has thus stuck as synonymous with June 6, 1944.

* footnote for longer explanation. In this way you prepare all you can with the plan, that is workable, and all other times are included, but in reference to an unset date / time, Such as 'On D-Day minus 4, the LCAs will arrive at assigned docks and begin loading ammunition and supplies. 'On D-Day minus 3, the LCTs will arrive at assigned embarkation points and will embark tanks and amtracks. 'On D-Day minus 2, troops will embark all amphibious shipping.' 'On D-Day minus 1, at H-Hour minus 23, all ships will pass reference point AF enroute

This question comes up every few months. It was a generic designation with no meaning outside the day the invasion starts. There was a D-day for every major Allied invasion i.e. Sicily, Okinawa etc.

This related to the basic principle of operational planning. Calendar dates could not be used for pre-invasion planning because the start date had to be flexible to adjust to weather, enemy actions etc. So all planning referred to days as D minus 2, D plus 3 etc.

The choice of D was simply an arbitrary (although reasonable) one. It had no deeper significance than that.

Reading some of Macs' major army invasions and battles D-Day was in common usage (D-10, etc.). Don't remember it's use with purely Marine/Navy battles though. Heh, not that my lack of memory signifies anything either way.

IIRC, Morison states that the landings on Leyte Island in the Philippines were made on 'A-Day' to avoid confusion with the Normandy landings.

This sounds stupid, but it is the accurate truth...

D stands for Day. H stands for Hour.

So, at 'D-Day, H-Hour, the invasion of France will commence...' which lets you say that 'D plus one we should have this accomplished, on D plus two, this, etc...'

This way, during planning you don't have to specify dates...