The problem with the Longest Day is he flubs the Rangers/Poine du Hoc story. Ryan never spoke to James Earl Rudder (who kind of ignored him because he didn't like one of his other books). So he wrote the story in the book, which is also in the movie, that the rangers climbed the hills to take out the German guns, but there were no guns, suggesting they wasted all of those lives.
Well that is true to a point, but only a point. The Germans had installed fake guns in the positions on the pre-invasion photos, but the real guns were still in the area, and had been moved to camoflage positions nearby. Rudder's team located them and destroyed them, thus completing their mission.