Mobster Carmine Ricca (Richard Devon) drives away from court and an angry mob after being acquitted on a legal technicality. An SFPD motorcycle cop stops Ricca’s limo for a minor traffic violation. Suddenly, the patrolman pulls his service revolver, shoots all four men in the car, and rides away.
Inspector Harry Callahan (Clint Eastwood) and his partner Earlington "Early" Smith (Felton Perry) visit the crime scene, despite being on stakeout duty. Callahan's superior, Lieutenant Neil Briggs (Hal Holbrook) dismisses them, seeing Callahan and his tactics as reckless and dangerous. Callahan, in turn, quips, "A good man always knows his limitations," mocking Briggs' pride in not ever drawing his gun in the line of duty. Callahan and Early then stumble upon a hijacking attempt at the airport; Callahan poses as a pilot and stops the two would-be terrorists.
Rookie cops Phil Sweet (Tim Matheson), John Davis (David Soul), Alan "Red" Astrachan (Kip Niven), and Mike Grimes (Robert Urich) encounter Callahan at an indoor firing range. Sweet, after demonstrating his speed and accuracy with Callahan's gun, reveals that he is an ex-Airborne Ranger and Special Forces veteran and that the others are as good or better shots than he. The young officers' zeal and marksmanship impress Callahan.
Later, a motorcycle cop slaughters a mobster's pool party using a satchel charge and a submachine gun. Shortly afterwards, a pimp (Albert Popwell) who murdered one of his prostitutes (Margaret Avery) is shot dead by another motorcycle officer. Callahan realizes that the pimp had let his killer approach him and offered a bribe. He deduces that a cop is likely responsible, and suspects his old friend Charlie McCoy (Mitchell Ryan), who has become despondent and suicidal after leaving his wife, Carol (Christine White).
Another motorcycle cop murders drug kingpin Lou Guzman (Clifford A. Pellow) and associates using a Colt Python equipped with a suppressor. However, Guzman is under surveillance and Callahan's old partner, Frank DiGiorgio (John Mitchum), sees McCoy dump his bike outside Guzman's apartment complex just before the murders. The motorcycle cop encounters McCoy in the parking garage and kills him to eliminate a potential witness. The motorcycle cop comes out of the garage to control the crowd, takes off his helmet and it is Davis. Meanwhile, at headquarters Harry presents his suspicions about McCoy to Briggs, who informs him of McCoy's death.
At the annual combat pistol championship, a puzzled DiGiorgio tells Callahan that Davis was the first officer to arrive after the murders of Guzman and McCoy. As Davis proceeds to break Callahan's speed and accuracy records, Callahan borrows Davis' Colt Python and purposely embeds a slug in a range wall. That night he retrieves the slug, and ballistics reveals that it matches those found at the Guzman and McCoy crime scenes. Harry begins to suspect that a secret death squad within the department is responsible for the murders.
Briggs ignores Callahan's suspicions and insists that mob killer Frank Palancio (Tony Giorgio) is behind the deaths. When Briggs obtains a warrant for Palancio's arrest and tells Harry to lead the raid, Callahan requests Davis and Sweet as backup. Palancio and his gang are tipped off via a phone call and arm themselves; in the ensuing gunfight Sweet is killed, along with Palancio and all his men. A search of Palancio's offices turns up nothing that would incriminate him, raising Harry's suspicions further.
The three remaining renegade cops confront Callahan in his garage complex. They present Callahan with a veiled ultimatum to join their organization: "Either you're for us or you're against us." He responds, "I’m afraid you've misjudged me." While checking his mailbox, Harry discovers a bomb left by the vigilantes and manages to defuse it, but a second bomb kills Early as Harry phones to warn him.
Callahan summons Briggs and shows him the bomb. While driving to City Hall, Briggs suddenly draws his revolver and forces Harry to disarm, revealing himself as the leader of the death squad. He cites the traditions of frontier justice and summary executions, and expresses disappointment for Callahan's refusal to join his squad. Grimes appears behind the car, following along as backup.
Callahan distracts Briggs by sideswiping a bus and beats him unconscious. Grimes gives chase and shoots out the car's rear windshield before Harry manages to run him over. The two remaining motorcycle cops appear and Callahan flees onto an old aircraft carrier in a shipbreaker's yard. As they stalk Callahan through the darkened ship, Astrachan shoots recklessly and runs out of ammunition, allowing Callahan to ambush and beat him to death. Callahan runs onto the top deck and starts up Astrachan's motorcycle, leading Davis in a series of jumps between ships before the two run out of deck space. Callahan manages to skid to a stop, but Davis falls to his death.
Callahan makes his way back to the car, but a bloodied Briggs appears, intending to prosecute him for killing the vigilante police officers rather than just shoot him dead. As Callahan backs away from the car, he surreptitiously activates the timer on the mail bomb and tosses it in the back seat. Briggs is driving away when the car explodes, killing him. "Man's got to know his limitations", Callahan quips again, before walking away.Clint Eastwood as SFPD Homicide Inspector Harry Callahan
Hal Holbrook as SFPD Homicide Lt. Neil Briggs
David Soul as SFPD Traffic Officer John Davis
Tim Matheson as SFPD Traffic Officer Phil Sweet
Kip Niven as SFPD Traffic Officer Alan "Red" Astrachan
Robert Urich as SFPD Traffic Officer Mike Grimes
Felton Perry as SFPD Stakeout Inspector Earlington "Early" Smith
Mitchell Ryan as SFPD Traffic Officer Charlie McCoy
Margaret Avery as the Prostitute
Bob McClurg as the Cab Driver
John Mitchum as SFPD Stakeout Inspector Frank DiGiorgio
Albert Popwell as the Pimp, J.J. Wilson
Richard Devon as Carmine Ricca
Christine White as Carol McCoy
Tony Giorgio as Frank Palancio
Maurice Argent as Nat Weinstein
Jack Kosslyn as Walter
Bob March as Estabrook
Adele Yoshioka as Sunny
Suzanne Somers as Pool Girl (uncredited)
Note: Harry's surname is spelled "Calahan" in the closing credits of Magnum Force. It is "Callahan" in every other film in the Dirty Harry series.
Writer John Milius came up with a storyline in which a group of rogue young officers in the San Francisco Police Department systematically exterminate the city's worst criminals, conveying the idea that there are even worse rogue cops than Dirty Harry. Terrence Malick had introduced the concept in an unused draft for the first film; director Don Siegel disliked the idea and had Malick's draft thrown out, but Clint Eastwood remembered it for this film. Eastwood specifically wanted to convey that, despite the 1971 film's perceived politics, Harry was not a complete vigilante. David Soul, Tim Matheson, Robert Urich and Kip Niven were cast as the young vigilante cops. Milius was a gun aficionado and political conservative and the film would extensively feature gun shooting in practice, competition, and on the job. Given this strong theme in the film, the title was soon changed from Vigilance to Magnum Force in deference to the .44 Magnum that Harry liked to use. Milius thought it was important to remind the audiences of the original film by incorporating the line "Do ya feel lucky?" repeated in the opening credits.
With Milius committed to filming Dillinger, Michael Cimino was later hired to revise the script, overseen by Ted Post, who was to direct. According to Milius, his script did not contain any of the final action sequences (the car chase and climax on the aircraft carriers). His was a "simple script". The addition of the character Sunny was done at the suggestion of Eastwood, who reportedly received letters from women asking for "a female to hit on Harry" (not the other way around).
Milius later said he did not like the film and wished Don Siegel had directed it, as originally intended:
Of all the films I had anything to do with, I like it least. They changed a lot of things in a cheap and distasteful manner. The whole ending is wrong, it wasn't mine at all. All movies had a motorcycle or car chase at the time — except Westerns. They have a scene where this black girl's pimp forces Drano down her throat. In the script, they merely went into the morgue and Harry said, "I don't feel bad for that son of a bitch, 'cause two weeks ago one of his girls was in here and he'd poured Drano down her throat." I think it's better to hear about it than to see it later; also, it goes right back to the character again: you understand Harry's feelings about it. All the stuff they put in about the Japanese girl: they put in a scene where the star gets to fuck some girl, and it's pretty hard to get it out. My Dirty Harry scripts never had Harry knowing any girls too well other than hookers, because he was a lonely guy who lived alone and didn't like to associate with people. He could never be close enough to a woman to have any sort of affair. A bitter, lonely man who liked his work
Eastwood himself was initially offered the role of director, but declined. Ted Post, who had previously directed Eastwood in Rawhide and Hang 'Em High was hired. Buddy Van Horn was the second unit director. Both Eastwood and Van Horn would go on to direct the final two entries in the series, Sudden Impact and The Dead Pool respectively.
Frank Stanley was hired as cinematographer. Filming commenced in late April 1973. During filming Eastwood encountered numerous disputes with Post over who was calling the shots in directing the film, and Eastwood failed to authorize two important scenes directed by Post in the film because of time and expenses; one of them was at the climax to the film with a long shot of Eastwood on his motorcycle as he confronts the rogue cops. As with many of his films, Eastwood was intent on shooting it as smoothly as possible, often refusing to do retakes over certain scenes. Post later remarked: "A lot of the things he said were based on pure, selfish ignorance, and showed that he was the man who controlled the power. By Magnum Force Clint's ego began applying for statehood". Post remained bitter with Eastwood for many years and claims disagreements over the filming affected his career afterwards. According to second unit director of photography Rexford Metz, "Eastwood would not take the time to perfect a situation. If you've got seventy percent of a shot worked out, that's sufficient for him, because he knows his audience will accept it."
The film would launch a number of careers, including David Soul (Starsky & Hutch television series), Robert Urich (S.W.A.T., Vega$ and Spenser for Hire) and Tim Matheson (Animal House and Fletch). Future Three's Company TV star Suzanne Somers can be seen as the topless blonde at the mobster's pool party.
The film received negative publicity in 1974 when it was discovered that the scene where the prostitute is killed with drain cleaner had allegedly inspired the infamous Hi-Fi murders, with the two killers believing the method would be as efficient as it was portrayed in the film. The killers said that they were looking for a unique murder method when they stumbled upon the film, and had they not seen the movie, would have chosen a method from another film. The drain cleaner reference was repeated in at least three other films, including Lethal Weapon (1987), Heathers (1989) and Urban Legend (1998). According to scriptwriter John Milius, this drain cleaner scene was never meant to be filmed, but was only mentioned in his original script.
In the film's opening weekend, it grossed $6,871,011. In the United States, the film made a total of $44,680,473, making it more successful than the first film and the sixth highest-grossing film of 1973.
Theatrical rentals were $19.4 million.
The New York Times critics such as Nora Sayre criticized the conflicting moral themes of the film and Frank Rich believed it "was the same old stuff". Pauline Kael, a harsh critic of Eastwood for many years mocked his performance as Dirty Harry, commenting that, "He isn't an actor, so one could hardly call him a bad actor. He'd have to do something before we could consider him bad at it. And acting isn't required of him in Magnum Force". Rotten Tomatoes sampled 20 reviewers and judged 80% of the reviews to be positive.