The beginning of Twelve O'Clock High has one very distinguishing scene: a bomber crew member has been shot in the head and somebody remarks that his brain is showing; another was parachuted out over France in the hopes that he'd get faster medical attention...even though his arm — which was blown off-- is still on the plane. Nothing is actually shown, but this kind of graphical detail was usually avoided by older Hollywood films. It's necessary to the plot of this film, however, because it establishes what men face when they fly off on bombing missions. Other than that, the first thirty minutes of the film are relatively average: Colonel Davenport (Gary Merrill) worries about pushing his squadron crews too far; the doctor (Paul Stewart) wonders how much a man can take mentally; and General Pritchard (Millard Mitchell) — on the advice of Brigadier General Savage (Gregory Peck) — replaces Davenport for fear that he's become too attached to his men.
The movie eventually takes off, and the exact moment occurs during an initially innocuous scene, after Savage has been chosen to replace Davenport. As he is driven up to the airfield, he stops and gets out of the front passenger seat. He offers his driver a cigarette and then slowly walks around the car. As he stands there smoking and staring off into the distance, you can't help but think, "What is this slow, pointless scene doing here? Get on with it." Suddenly, Savage and the driver put out their cigarettes and Savage gets into the back seat. It's an effectively understated moment that tells us Savage has consciously and deliberately just taken on the mantle of the tough guy commander. And sure enough, the first solider he meets (Kenneth Tobey in a bit part) gets chewed out for lax security.
What follows is a series of scenes in which Savage brings discipline to the squadron. (These "whip the troops into shape" sequences are not foreign to war movies, but they never seem to get old.) Savage is so unpopular — especially compared to Davenport — that all the pilots ask for transfers. In more private moments, Savage reveals his need to have the pilots change their minds about him, to have them realize that his strictness is good for the squadron. But Savage seems too needy. It's too much of a contrast with the coldness he usually shows as the commanding officer. But this sharp contrast is only setting up the viewer for what happens later.