Early in the film, Andy is seen in a football game on TV. As he's about to kick the ball, the screen shows a close-up of him from immediately below and in front of him. But no TV broadcast of that era would have had a camera on the field in such a position to get that shot.
It is not an error that several of the soldiers seen in this film are wearing other unit patches on their right sleeves. They are all wearing the 5th Infantry diamond on their left sleeve. A soldier's current unit is always worn on the left sleeve. Those soldiers who are combat veterans are authorized to permanently wear the unit patch of the unit they fought with on their right shoulder. So all those patches on the right sleeves represent units those men served in during World War II or Korea.
Semper Fidelis (Always Faithful) is the motto of the U.S. Army's Eleventh Infantry Regiment, as well as the motto of the U.S. Marine Corps.
During a live fire mortar exercise, the crews would never be set up so close together. There are many things that can happen when sending mortar rounds down range. The setup seen in this movie would be dangerous to all involved.