What Does The D In D Day Stand For

It seems everyone has a theory—debarkation day, decision day, even doomsday. But the truth is really much more boring. Used since WWI, the D merely means the generic day of an invasion, says Nick Mueller, director of the National D-Day Museum. The code terms D-Day and H-hour are used so the date and time of an operation can be kept secret (and so plans don’t have to be rewritten if the mission is postponed). Technically, there have been countless D-Days in military history. But for most of us, since the invasion of Normandy on June 6, 1944, there’s only one. —Sally Atkinson