Not to be knit-picky, but, Denis Leary's character was not a lieutenant. He was a "Chief Warrant Officer Grade 3", or "CWO-3" for short. If there is any question of this, one should check out the close-up of Leary to note the bar on his collar with 3 black squares on it.
Should also be noted, wearing of the Beret with colored insignia and flash (patch), was not done during combat operations. The last thing anyone wanted was to be seen because there was something shiny or colorful which could give away one's position to the enemy.
Aside from those inconsistencies, Disney did a great job of putting this motion picture together.
The people chosen, did a fantastic job of being as authentic as possible. Of course, much about the real story had to be quieted down for the sake of the audiences viewing pleasure. Since the real truth of the war was the horror of confrontation.
This was an awesome film, which helped to show an aspect of people in the military, as people. And not the mindless drone killers, some in the population would have the world believe. There was much humanity by the armed forces, but, those are the news stories which the networks DIDN'T show, because it didn't have the flair and sensationalism that was desired by the various network news casts.