Much of the movie is based on historical anecdotes. For example, the part about issuing cigarettes and the GI responding, "No thanks, I don't smoke" to which the quartermaster replied, "Take them, after this you will."
I read "D-Day" by Stephen Ambrose and you realize most of the stories seemed to be pulled directly from his historical account.
One other inaccuracy was when Tom Hanks called the "Panther" a "Panzer". "Panzer" is the German word for "Armor".
To add to the "D-Day" definition, there is also "H-Hour" and so forth. All time is reference to the attack date. IE, before the attack the countdown does from D-Day - 5, D-Day - 3, etc.. Days subsiquent to the attack are D-Day + 1, D-Day + 2.
Windogg