In St.-Lo, at the headquarters of the 84th Corps, Major Friedrich Hayn, the intelligence officer, was making arrangements for another kind of party. He had ordered several bottles of excellent Chablis, for at midnight the staff planned to surprise the corps commander, General Erich Marcks. His birthday was June 6.
They were holding the surprise birthday party at midnight because Marcks had to leave for the city of Rennes in Brittany at daybreak. He and all the other senior commanders in Normandy were to take part in a big map exercise that was to begin on Tuesday morning. Marcks was slightly amused at the role he was supposed to play: he would rpresent the "Allies." The war games had been arranged by General Eugen Meindl, and perhaps because he was a paratrooper the big feature of the exercise was to be an "invasion" beginning with a paratroop "assault" followed by "landings" from the sea. Everyone thought the Kriegsspiel would be interesting - the theoretical invasion was supposed to take place in Normandy.
The Longest Day is Cornelius Ryan's history of D-Day, published about fifteen years afterwards. It's not just a history of the event, but a story of the people involved - occupied French, Allies, and Germans.
He wrote it based off of official reports and countless interviews with people who had been there on all sides. There's so much in here that gets you down on the ground with people, so much showing how personal it all could be, how the fog of war affected things, and all the strange quirks of that day. It's amazing, tense, horrible and uplifting by turns. Several times, it moved me to tears.