South Korea, Autumn 1951. The 4077th Mobile Army Surgical Hospital receives two new replacement surgeons: the down-to-earth Captain "Hawkeye" Pierce (Donald Sutherland) and the good ol' boy Captain "Duke" Forrest (Tom Skerritt). Upon their arrival, it quickly becomes evident that they are a pair of mischief-makers who have a penchant for breaking the rules and charming the nursing staff, having even "borrowed" a Jeep to make their entrance. Despite their troublesome antics, they are efficient in their surgical duties.
However, they soon find themselves at odds with their tent mate Major Frank Burns (Robert Duvall), a pious man who isn't quite up to par as a surgeon. Hawkeye and Duke exert pressure on Lt. Colonel Henry Blake (Roger Bowen), the stern commanding officer, to have Burns removed from their shared living space. Concurrently, they urge him to request the assignment of a skilled thoracic surgeon to the 4077th.
Just days later, a mysterious new thoracic surgeon, Captain "Trapper" John McIntyre (Elliott Gould), makes his entrance, providing little information about himself. Hawkeye reminisces about a college football game, recalling how he managed to score the only touchdown by intercepting a pass from Dartmouth's quarterback, who happens to be Trapper.
As tensions rise, Major Margaret Houlihan (Sally Kellerman), the newly appointed chief nurse of the camp, arrives and is promptly introduced to Colonel Blake. During her tour, Trapper observes Burns wrongfully blaming a naïve Private Boone (Bud Cort) for a patient’s death. Things escalate when Trapper confronts Burns openly, striking him in front of both Houlihan and Blake.
Though Major Houlihan is a skilled nurse doing her best to assist during surgeries, her interactions with Hawkeye become strained. In a chance meeting at the mess hall, both begin to express their discontent for each other; she perceives Hawkeye as a reckless idealist while he calls her a "typical, uptight, career-army clown."
A week later, while Colonel Blake is away, the camp celebrates Trapper's promotion with a raucous party. Burns and Houlihan are appalled and, in an act of recklessness, they surrender to their own desires, engaging in a sexual encounter that’s indiscriminately broadcast via the PA system. This gives rise to Houlihan being dubbed “Hot Lips,” a moniker she does not take lightly.
When Colonel Blake returns, Hawkeye humorously taunts Burns about the prior night's events, provoking a fight between them that leads to Burns being declared unfit for duty and sent away never to return.
Meanwhile, Father Mulcahy (René Auberjonois), the camp chaplain, becomes privy to the struggles of "Painless Pole" Waldowski (John Schuck), the camp dentist, who confesses to a crisis in his love life. In a comical turn, the group stages a "Last Supper" for Waldowski, leading him to believe he has a terminal condition, all while Hawkeye sets up a rendezvous to help him regain his confidence.
The prankster duo of Hawkeye and Duke continue to stir up trouble, including a scheme involving the chief nurse, Hot Lips, which results in her exposure in the shower tent, leaving her humiliated. Angered, she commands Colonel Blake to restore order to the camp.
The narrative takes a poignant turn when Ho-Jon (Kim Atwood), a local boy working at the camp, is drafted into the South Korean army, sparking a series of events that underscore the realities of war. Hawkeye's efforts to protect him lead to tragic consequences when, after surgery, Ho-Jon is left wounded in action, a bitter reminder of the fleeting nature of life amidst chaos.
In a more light-hearted subplot, Hawkeye and Trapper are sent to Japan for an urgent surgery on a U.S. Congressman’s son, leading to a day filled with golf and camaraderie but swiftly followed by further complications. Upon returning to the 4077th, they find new relationships having blossomed among the staff as Duke and Hot Lips take their budding romance public.
As tension mounts with the arrival of General Hammond, a football game is set to test the mettle of the 4077th against tough opponents. With a hefty bet riding on the game, Hawkeye and his friends pull out all the stops, enlisting the help of an ex-professional football player to widen their chances.
The match is intense and comedic, filled with strategy and camaraderie, culminating in a last-minute play that secures their victory and the resulting celebration reminds everyone of the joys of friendship amidst the harsh realities of war.
Finally, with discharge orders in hand, Hawkeye bids farewell to his friends and the camp. Duke shares a heavy-hearted goodbye with Hot Lips, while Trapper stays behind. Together, Hawkeye and Duke drive away in the very same jeep they took upon their arrival, the camp slowly fading into the backdrop as the PA system announces the end, echoing the bittersweet essence of their shared experiences.
