If you're interested in military history, you may have seen or read the work of Stephen Ambrose. He was one of the world's foremost experts on warfare, and unsurprisingly Spielberg consulted him when he was putting his masterpiece together. If you want to make something authentic, it's wise to seek the opinions of those who know the most about your subject matter.
Spielberg wanted to make sure he'd got the film just right, and so arranged a special screening of the movie for Ambrose before the general public got to see it. Twenty minutes in, Ambrose walked out. It's not that he hated the film; quite the opposite. It was so realistic and so intense that it impacted him profoundly. He took a pause to compose himself and prepare his mind to endure the rest of what he was going to watch, and then went back in to finish the job. Needless to say, he gave it his seal of approval.