When the characters use an Army Saber to salute, they all fail to do it correctly except Sean Penn while on horseback. It is a two-step maneuver. On the preparatory command of "PRE_SENT", the saber is brought to a position approximately four inches from the soldier's nose so that the tip of the saber is six inches from the vertical. The soldier is looking at the flat side of blade at the top of the hilt and the blade is either straight up or slightly tilted forward. The actors do this part correctly. What they fail to do is at the command of execution "ARMS", the right hand is lowered with the flat of the blade upward, the thumb extended on the left side of the grip and the tip of the saber about six inches from the marching surface and pointed at the ground. Assuming the actors received the same instructor at Valley Forge Academy, they must have all been taught this way. It is not, however, in accordance with Army Regulation FM 22-5, now called FM 3-21.5.
When Ronnie Cox's character is shot by Capt. Shaun, he appears to be hit in the left side of his neck. Later he is holding is left shoulder. When he is phoning in for the copters to lay down the smoke, a soldier is shown applying a bandage to his right arm. By the very end, there is no sign of any gunshot injury or bandage.
The M-16s the cadets use throughout the film are all loaded with the old style 20-round magazine yet, at the film's end, one cadet is seen carrying a weapon clearly loaded with the longer, curved 30 round magazine.
When Timothy Hutton and Sean Penn get into a fight after their altercation in the senior lounge, three railings from the stair banister are clearly knocked out. At the end, when the two speak, the railings are back in place again.
When the cadets are confronted by the townies after one of the trucks stalls, as the cadets are racing back to the second truck, a wheel chock can be seen in front of the forward wheel of the rear axles on the right hand side of the truck.
When all the adult staffers of Bunker Hill Academy are loaded onto the bus, we see a Captain and a few other uniformed soldiers. Bache's statement that the Cadet Major is only outranked by the commanding general, then, is untrue. Active military personnel outrank ANY cadet in a K-12 military academy.
When Brian tells Kerby that he'll surrender if General Bache orders him to, Kerby says that General Bache died at 6 o'clock yesterday. In a military case, he would have said that the General died yesterday at 1800 hours.
When taking inventory of the armory, the man counting the weapons states they are ".45 millimeter caliber 1911's". M1911 pistols are .45 caliber, meaning the bore is .45 inches in diameter, and not the metric measurement of 45 millimeters (a significantly larger measurement, to the point where they would be classed as artillery, rather than small arms). In countries which issued the M1911 (or copies), and to whom the Metric system was common, the cartridge was referred to as 11.43x23mm.
During the final battle when Shawn begins his shootout with the National Guard/SWAT the M-60 he uses is loaded with a single belt with about 50 rounds of ammunition on it. Yet he fires long burst for several minutes during the gunfight with no pause. The cyclic rate of the M-60 would have run through that much ammunition in a few seconds.
When the townie youth is shot, it is actually the youngster on the general's (George C. Scott's) back that is holding the gun, not the general, though everyone, including the general, indicates the general shot him. The gun is in the general's hand when the camera pans back after the shooting.