What is D-Day all about?
“D-Day” was the day of the beginning of the Allied inavasion of Europe for the purpose of driving out the Nazis. It was the largest amphibious assault ever. While the overwhelming scope of that operation has given the term “D-Day” that special significance, it originally was, and still is, rather mundane military terminology for a target day in planning a campaign, in the same way the term “H-Hour” is sometimes used. The terminology makes it possible to do the planning without reference to actual calendar dates, partly for reasons of operational security, and partly because that daate might not be finally chosen until late in the process. So in the scheduling of events, it would look like a countdown: D-Day-minus-10, D-Day-minus-9, and so on as preparations are made, up until the day the operation began, D-Day, followed by D-Day-plus-1, D-Day-plus-2, which would deal in goals for the operation and the ongoing support.
