When Lt. Wattsberg walks into Major Barker's office to tell him that they got the air support they needed, Barker was reading a book called "Seven Firefights in Vietnam", which wasn't published until 1970.
Both Corporal Coucey and Corporal Lincoln salute Major Barker incorrectly when they report to him for duty. Instead of saluting, waiting for the major to return the salute, then dropping theirs, both men quickly drop their salutes before Barker even begins his.
Burt Lancaster (Maj Barker) was about 64 years old when this movie was made. No real Army major would be able to stay in the service until that advanced age. He would have been retired at a much younger age as a result of being continually passed over for promotion, as Major Barker had been.
Major Barker tells his executive officer that he served in Korea during the Korean War, yet he wears no Combat Infantryman's Badge. He would have earned a CIB for his infantry service during that earlier war.
At the very beginning of the movie during the credits and the overview of the camp and right after the title shot, if you look in the far background at the top of the scene you can see what looks like traffic and cars passing by.