Just what is a “D-Day,” exactly?

The origins of the phrase

Second Lieutenant Walter Sidlowski after the rescue of several soldiers from a damaged landing craft on Omaha Beach on D-Day+1
(Photo: U.S. Army)

You know about D-Day: June 6, 1944, when Allied forces landed on the shores of Normandy to being the liberation of Nazi-occupied Europe. It’s the single best-known date not only in the history of World War II, but likely in all of military history. But do you know why it is called “D-Day”? What does “D” stand for? And did you know that there were actually several D-Days? Today’s article is about the origins of D-Day’s name.
There’s a bit of confusion about the actual meaning of the “D” in “D-Day.” One popular view, often repeated in France, is that it stands for “disembarkation” or “debarkation” and refers to the invading Allied troops disembarking from their landing craft. Other, more far-fetched explanations also sometimes heard in America is that the letter stands for “decision”, “deliverance” or “doom.”  None of these ideas, however, hold any water.

American troops and trucks coming ashore on Omaha Beach
(Photo: U.S. military)

As we have already written about it before (Read our earlier article – What’s in a code name?), the Allies took great pains to give their operations proper code names. This meant the code name was not supposed to be indicative of the nature of the operation, such as the name of a fish species standing for a marine operation. With the imminent Allied landings somewhere in Europe, and its obvious importance, an overdramatic code name such as “deliverance” would have been unacceptably likely to tip off the Germans.
Another aspect of code name selection was to avoid both levity, which would be inappropriate for an event where a lot of people were likely going to die, and a sense of despondence that might hurt the soldiers’ morale. Just think about it: if you were a soldier who wanted to go home and see his family one day, how would you feel about being told to fight in something called “Dooms-day”?
So, if these words aren’t the origins of “D-Day,” then what word is? Someone actually asked that question in 1964 in a letter addressed to former President Eisenhower, who served as Supreme Allied Commander during World War II. The letter was answered by Eisenhower’s executive assistant, Brigadier General Robert Schulz, who wrote: “General Eisenhower asked me to respond to your letter. Be advised that any amphibious operation has a ‘departed date;’ therefore the shortened term ‘D-Day’ is used.”

Former President Eisenhower (left) and Robert L. Schulz (right)
(Photo: Harry S. Truman Library)

“Departed date” thus comes from a rather authoritative source, but it still doesn’t paint a complete picture. To be fair, Schulz’s statement probably reflected how the phrase was understood during the planning of amphibious operations, but its historical use doesn’t seem to fully support the claim.
As far as it can be determined, the U.S. military first used the term “D-Day” decades before World War II. Field Order Number 9 of the First Army, part of the American Expeditionary Forces led by General John Pershing,
(Read our earlier article - The General of the Armies) and fighting in Europe during World War I, was dated September 7, 1918, and referred to a planned attack: “The First Army will attack at H hour on D day with the object of forcing the evacuation of the St. Mihiel Salient.” The attack on the German-held area protruding into French lines started on September 12 and was the first and only offensive of the war launched entirely by American troops. Catching the Germans mid-retreat and with their artillery out of position, the battle saw the First Army victorious, thanks in part to the exploits of then-Lieutenant Colonel George Patton. (Read our earlier article – The wars of George S. Patton)

An American artillery crew manning a 75 mm gun on the first day of the Saint-Mihiel Offensive
(Photo: National Archives and Records Administration)
A brief anecdote about this first D-Day is in order. During the battle, Patton happened to meet Brigadier General Douglas MacArthur, another officer who reached the apex of his fame in World War II, on a hilltop. As they were talking, the Germans launched a “creeping barrage” in their direction. A creeping (or moving) barrage is a type of artillery attack where shells are launched along a line. Once they hit, a second line, further away from friendly positions, if shelled the same way, followed by a third, fourth and subsequent lines of destruction, with each line getting closer and closer to the enemy. This technique is normally paired with the attacker’s own infantry and armor advancing behind the moving line of destruction, so they’ll reach the enemy trenches just after the last barrage hit.
A Renault FT-17 tank in the Saint-Mihiel Offensive
(Photo: Library of Congress)

It was such a barrage that was approaching the hill on which Patton and MacArthur were standing, with each series of explosions hitting ever closer. Both officers had a reputation for fearlessness and neither wanted to flinch in front of the other, so they ignored the approaching peril and carried on their chat. Eventually, to their great luck, the barrage passed over them, leaving both men unharmed as they were standing in the narrow safe spot between two bursts. Patton later wrote: “I think each one [of us] wanted to leave but each hated to say so, so we let it come over us. We stood and talked but neither was much interested in what the other said as we could not get our minds off the shells.” He also noted that “I was the only man on the front-line except for General MacArthur who never ducked a shell.”

MacArthur and his staff observing the battle during the Saint-Mihiel Offensive
(Photo: U.S. Army)

What is perhaps more relevant to this article, however, is that the Battle of Saint-Mihiel was in no way an amphibious operation, which means that Schulz’s 1964 statement about “D-Day” in incomplete, though it must have reflected his own understanding. The explanation accepted by the military today is that “D” simply stands for “day” and H for “hour.”
The terms D-Day and H-Hour were used in numerous operations, as they made planning easier. Large, complex operations must be planned in great detail and comprise numerous timetables and deadlines. These timetables have to be created long before the actual starting date and time of the operation is settled, so terms like D-3 (three days before D-Day) or H+6 (six hours after H-Hour) are used in the plans in lieu of fixed times. Additionally, if an operation starts early or late (and Operation Overlord itself had to be delayed a day due to bad weather), such timetable won’t need to be rewritten, since the relative time designations will remain correct.

Eisenhower’s draft for the orders of the day on June 6, 1944
(Photo: Eisenhower Library)
U.S. military plans from World War II show that the terms “D-Day” and “H-Hour” saw use numerous times before the most famous example of June 6, 1944. The landings in Normandy, however, were such a major and symbolically important effort that their very existence caused a decline in the use of the phrases in other areas of operation. With so much effort, supplies, transport capacity and personnel tied up in the landings in Western Europe, other major operations in the same year received different codes for their own starting times to avoid confusion. Thus, the October 20, 1944 invasion of the Island of Leyte in the Philippines started on A-Day, while the first day of the landing on Okinawa, on April 1, 1945, was L-Day, for “landing.”
MacArthur coming ashore at Leyte on A-Day
(Photo: National Archives and Records Administration)
X-Day was planned to be the beginning of the invasion of Japan and the first landings on the island of Kyushu in November 1945, and Y-Day was going to be the landings on the mainland of Honshu and the invasion of the Tokyo Plains in March 1946; of course, these attacks never manifested due to the war ending. J-Day was used as a general term for the date of specific assaults in both world wars. Z-Day was the landing of Australian forces to liberate Brunei in North Borneo on June 10, 1945, and Q-Day was June 23, 1945, the rehearsal for Trinity, the first atomic bomb test.
Similar date and time designation exist to this day. For example, E-Day is the starting date of NATO exercises, K-Day is when a military convoy system is established along a route, M-Day is the date of mobilization, and N-Day is when a unit is notified for deployment or redeployment.

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An Independence Day-related propaganda poster from 1943
(Photo: Office of War Information)
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