When the crowd of soldiers is gathered around watching the brawl between Private Prewitt and Sergeant Galovitch, many of the men, including Private Prewitt, have the acorn cords on their campaign hats tied in knots. This is only done by combat veterans, and since the war hadn't started yet, none of the junior enlisted men would have served in combat. Therefore, nobody in that scene, and especially Private Prewitt, should be wearing their campaign hats with the acorn cord tied in a "combat knot".
At the beginning of the scene in which Buckley first talks to Prewitt about his situation, Prewitt's line, "You know anything in army regulations says I gotta box?"- has obviously been dubbed over a different line - his mouth movements don't match those words.
Throughout the film, the hairs on Prewitt's chest are plainly visible when the top of his shirts are open, but when he's shown without a shirt in Alma's house, all his chest hair has been shaved, which was the usual practice in 1950s Hollywood films.
During Sgt. Warden's visit (pretending to look for Capt. Holmes), Karen tells him that she will phone her husband and walks to the dining room. When she stands in the doorway, we see two chairs inside, on the left. In the next shot, they both enter the room and the chairs are not there.
In the bar fight scene between Fatso and Maggio, Sgt. Warden breaks a bottle to use as a weapon to threaten "Fatso" and to stop the fight. Eventually he throws the bottle, apparently outside through an off stage, unseen door (he throws the broken bottle across the room). Later, the smashed bottle is visible on the table in a close-up.
The soldier removing the boxing memorabilia from the captain's office walks toward the doorway where several other soldiers are gathered. He, apparently, vanishes before he ever makes it out the room, since the following shot is of the crowd of soldiers, and he is nowhere to be seen.
After the bar fight, Warden kicks the flick knife way off to the left, away from the bar. But Prewitt is then seen picking up the knife next to his table off to the right, towards the other end of the bar.
Towards the end of the movie, there is a long shot showing a very drunk Prew sitting down in a dirt road next to Warden. Prew then crosses his legs. In the medium shot following, we see that the wrong leg is crossed in front of the other.
When Private Maggio is dressing and using the talcum powder, he's holding it with his right hand after the last soldiers leave and then powders his left arm. In the next shot immediately after, he's placing it on a shelf in his locker with his left hand.
1st Sergeant Warden is actually wearing the correct stripes. Modern 1st Sergeant stripes have a three up-three down configuration. However, from 1920 to 1942, 1st Sergeants had three chevrons and only two rockers, along with the center diamond. The modern version with three rockers was adopted in 1942, after the attack on Pearl Harbor.
A bugler who is as good as Prewitt would never become a boxer for fear of messing up his embouchure if he were hit in the mouth. If he's that good he'd never risk screwing up his livelihood in civilian life.
The goof items below may give away important plot points.
When the officer and First Sergeant Warden are conversing over Private Prewitt's body, the officer calls First Sergeant Warden, "sir". In the United States Army, noncommissioned officers are never called, "sir". Only commissioned officers and warrant officers are addressed as "sir".
When Sgt. Warden is on the roof machine gunning Japanese planes, he is holding the gun by the barrel which, after a few rounds, would be too hot to handle.
The machine gun has an asbestos glove used to switch the barrel when it gets too hot. Sgt. Warden is using the glove to hold the barrel.
In the close-ups of the newspaper articles about the search for Sgt. Judson's murderer, read by Warden and Lorene, it's obvious that that story has been pasted over a real newspaper article and that everything after the lead paragraph is taken from an altogether different article, since after the first paragraph none of the text has anything to do with the Judson story, and even the typeface is entirely different.