It has elements of all the generic conventions. Frank Lovejoy is the Marine colonel who has to whip his battalion of raw recruits (is there any other kind?) and retreads into shape. His tactic for achieving this is to morph into Frank Lockjaw. Only towards the end does he begin to show his more sensitive side. Yes, on the surface he may be crusty and hard-hearted. But underneath that, he's a real softy. It's a good thing they didn't dig any deeper into his character or they might have found another layer in which he was a real MEAN SOB.
Richard Carlson is the retread from World War II, a reservist pulled back into active duty as a company commander. He's forced to move his wife and two lovely kiddies into a Quonset hut and he's deprived of their company, despite his whining to Lockjaw. He toughens up though and learns to be a Marine first.
There is the kid, Russ Tamblyn, who at this stage of his career could not yet act, who must prove himself as much a Marine as the rest of the men in his family. (He looks about fourteen.) One of his brothers is an officer serving near Tamblyn's unit and we know at once, when Tamblyn asks for permission to visit after a battle, that the brother is KIA.
Then there is the somewhat slow, drawlin' Southrin boy who provides a bit of comic relief, though not much. And the Gunnery Sergeant who must harden his men for battle.
The usual conventions are followed. There is the mail call ritual, the fierce climactic speech about how we'll fight on and reach our goal, outnumbered and surrounded though we may be. The final entrance of the troops and equipment into Allied lines. And when some bystanders ask this ragged group what outfit they belong to, Frank Lovejoy (now thoroughly humanized) straightens up and replies proudly, "First battalion, United States Marines." It really does hark back to World War II movies. The enemy are faceless. The rifle shots don't sound like rifle shots at all. A fired weapon emits a modest ka-Whoosh instead of a loud pop. There is the tension of waiting while the enemy approach like black cockroaches over the snowy hills and our troops are out of ammunition until, at the last moment, the skies clear and cargo planes make the necessary drop, just as in "Battleground", a superior example of the genre.
Some of the engagements are shot in the hills around Hollywood, but there is some combat footage from Korea inserted too. The actual events have been cleaned up a bit for public consumption. The reason the Marines and the Army had been caught with their pants down is that they had sailed northward through the British lines as if on a picnic. MacArthur had found little resistance in North Korea and was determined to thrust quickly through to the Manchurian border, while the more prudent British adopted a cautious advance on a broad front. MacArthur had assured President Truman that there was no chance of Chinese intervention, a big misjudgment. MacArthur had also declared the men would be home by Christmas which didn't happen and this is mentioned by one or two characters in the film, but sadly, without bitterness. The retreat from the reservoir was genuine hell. The weather was bitterly cold and frostbite was common. The Chinese troops had more protective clothing than ours. And omitted from this movie are newsreel scenes of frozen bodies being dragged on sleds behind trucks during this slow, sixty-mile retreat.
I'd give this movie bonus points for having taken a chance on its being about a retreat instead of a victory. We don't hear much about Korea these days. It ended in a stalemate. Retreats, defeats, and stalemates are the stuff neither of legends or commercially successful movies. They don't follow the accepted scenario in which we either win or put up a gallant fight before being wiped out by a treacherous foe. "A Bridge Too Far" was another risky production. I doubt that this one would have been made in quite the way it was except for a proclamation by one Marine officer who, when asked if they were retreating, said, "Retreat, Hell. We're just advancing in a different direction." A ringing line like that is enough to transform our perception of what we are witnessing on the screen.