What is the D in D-Day?

My mother claims the D means Day which would put the whole expression as Day-Day which sounds retarded.
It seems more likely that there were A, B and C days and D-Day was just the next in a sequence.
What’s the dope?

Never underestimate the knowledge of mom. D stands for ‘day’.

D-Day, H-Hour…

Nothing creative.

“D-Day” and “H-Hour” are military designations for the time at which an operation is due to commence. The “D” and “H” don’t actually stand for anything, other than an indication that it’s a particular or special time. Thee term “D-Day” is popularly associated with the Normandy Invasion and Operation Overlord, but the term is used generically in other major operational events as well.

There is a famous “A-Day” in WWII, but it actually occured after the invasion of Normandy, and in the Pacific theatre, with the famous (or infamous) Invasion of Leyte, starting 17 October 1944, as part of MacArthur’s campaign to retake the Philippines and get some spectacular wading ashore footage in the bargin. (The famous shot at Palo Beach had to be recreated several times until it met MacArthur’s satisfaction.) There are other alphabet days designating various types of activites, though no specific standard, and for most the preceding letter bears little resemblence to the activity thereby described.


The use of “D-Day” and “H-Hour” allows you to set goals and plan without knowing the exact date of your project. You can say, “at H plus 2 hours, we want to have secured the beach-head.”

It’s the exact same as the shuttle countdown, with “T minus 10 seconds.” The shuttle launches at T-Time.

That’s four O’clock isn’t it?

In French it’s J-Jour

It seems that lately, they’ve been launching at Miller time.



Would I be correct in assuming that this generic method serves security purposes as well? After all, you wouldn’t want the other side to know what day you intend to strike in case they intercepted communications.

As said, nothing much. The first of use of the term was in a US Army document from WWI. Also as stated it is J-Jour in French.

M-Day is the day of mobilization. Other days have their own letters. Oddly the use of D-Day is less so since 6 June 1944 has preempted the term.

Actually, it is Jour-J. And for the invasion of Okinawa, it was L-Day.

I can see why. It’s really strange to hear 1943 footage (after the action, of course) referring to the invasion of Tarawa on “D-Day,” if you’re not used to it.

“Love Day” for Operation Iceburg Easter Sunday, 1 April 1945. “Love” was then the radio phonetic used by the military. Oddly no documents seemed to call D-Day “Dog Day.” Go figure.

X Day was the planned day for the invasion of Japan.

Only if the golf course is ridiculously overbooked that day.