In military terms, D-day typically refers to the day on which a very crucial activity is planned to begin. Historically, the day of 6 June, 1944 is known as the D-Day. This was the day on which an enormous assault was staged by the Allied forces against the Germans. The origin of the term D-day is known by very few people.
Different people have different views about what the ‘D’ in D-Day actually stood for. A majority of historians and scholars argue that it was just a random alphabet used for the purpose of identifying the day. Others have proposed that it denotes ‘departure’, ‘decision’ and also ‘doomsday’. According to the U.S military itself, the D in D-day means nothing and is merely an alliterative placeholder used to nominate a specific day on calendar.
D-Day as a term had been used to denote a special military occasion well before the World War II. However, after the World War II, the term almost became synonymous with the date June 6, 1944. This was the day of the Normandy landings when the Allied forces launched their counter-offensive.
The term ‘D-Day’ was also being used by the armies during the World War I. This is reflected in one particular field order of the American First Army which participated in the war. The order mentioned that the said army would attack the Mihiel salient on D-Day and H-Hour. Similarly, the British military deployed terms like ‘Z-Day’ and ‘Zero Hour’ to denote the launch of a particular assault or attack. France forces made use of terms like ‘Le Jour J’. These instances reinforce the belief that the ‘D’ in D-Day really signifies nothing and is merely an arbitrary alphabet.
In the military terminology, D-day is the day on which a massive attack is to be initiated. In the same way, H-hour is the hour on which the attack is scheduled to begin. The earliest use of these terms was found in World War I by the U.S. Army center of military history.
The D-day for the invasion of Normandy was initially set for June 5, 1944, but was delayed until 6 June due to bad weather and heavy seas.
However, there was one D-day and one H-hour for all the units participating in the gigantic operation. This shorthand actually helped the Allies to keep the date of the operation a secret and prevent the Nazis from knowing about it. It also allowed various Allied units to coordinate their operations without knowing exactly when the attack was to take place. To denote events near the D-Day itself, Allies military commanders used terms like D+1 or D-1.