'Saving Private Ryan' has the grain of military truth running right through it. It was made to honor a real soldier, the cast were trained by real soldiers, and the extras were largely made up of real soldiers. There were also many real soldiers involved as advisers to the film, helping Spielberg to ensure that his scenes stayed close to the truth.
One of those advisers actually ended up on screen in a small role. An older man with a moustache appears as a War Department Colonel at one point to advise General George C. Marshall not to send a rescue party after Private Ryan. If you're going to have a senior military figure in your film offering advice and giving orders, you might as well go with someone who truly knows what he's talking about! The movie is loosely based on real life events involving the capture and recovery of a private, and there were those involved in those events who didn't feel the exercise was wise.