D-Day Definition: What Is the Meaning of D-Day?

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American troops land on Utah Beach, Les Dunes de Madeleine, France on June 6, 1944 to come as reinforcements to those already stationed. (STF/AFP/Getty Images)

June 6, 2015 is the 71st anniversary of the Normandy beach invasion by American and allied forces against Nazis in 1944 France. But what does the “D” stand for? It does not stand for “disembark.”

In military terminology, “D-Day” is the day on which any given combat operation begins. Therefore there has been more than one D-Day throughout history, but “Operation Overlord”, which began on June 6, 1944, is the most famous of these. The “D” in “D-Day” does not stand for anything but is instead used as an indicator to points of time before or after a combat operation begins. For example, D+1 means 1 day after D-Day. H-Hour is also a term used and references the hour on which any given combat operation begins. According to the U.S. Army Center of Military History:

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.

Throughout history there has been A-Day through Z-Day, with only “B-Day” skipped over. Each “Day” with a letter before it as its own militaristic meaning for days and hours. To see a complete list of military designation of days and hours, click here.

The invasion of Normandy on D-Day was the largest seaborne invasion in history and helped free France from Nazi control. It ultimately aided in the Allied war victory, too.