When a military operation is being planned, its actual date and time is not always known exactly. The term "D-Day" was therefore used to mean the date on which operations would begin, whenever that was to be. The day before D-Day was known as "D-1", while the day after D-Day was "D+1", and so on. This meant that if the projected date of an operation changed, all the dates in the plan did not also need to be changed. This actually happened in the case of the Normandy Landings.
The Great Lakes Coast Guard is sharing the story of Petty Officer 3rd Class J.J. MC Andrews on his journey across the Atlantic Ocean into the Mediterranean Sea for the invasion of Italy, then to the shores of Normandy for D-Day, in our five-week series “World War II combat diary of J.J. MC Andrews.”