According to writer John Milius, the reason the sex scene with the Asian woman "Sunny" (Adele Yoshioka) is in the script is because Clint Eastwood received many fan letters from Asian women that contained sexual propositions.
Directly after the scene in the garage where Callahan is threatened by the motorcycle cops, the cycles drove out and every single one of them crashed. Clint Eastwood said, "I've been threatened by the Keystone Cops."
When Clint Eastwood approached Don Siegel to offer him the directing job for Dirty Harry (1971), Eastwood gave Siegel four drafts of the script, one of which was written by Terrence Malick. In Malick's script, he changed the killer from being a mindless psychopath killing because he likes it, to being a vigilante who killed wealthy criminals who'd escaped justice. Siegel didn't like Malick's script, but Eastwood did. Malick's ideas formed the basis for Magnum Force, the second film in the Dirty Harry series.
Clint Eastwood declined the director's seat, and Ted Post stepped in, although interviews with Eastwood and books about him have indicated that he and second unit director Buddy Van Horn actually directed more of the film than Post did. Post had earlier directed Eastwood in several Rawhide (1959) episodes and the feature Hang 'Em High (1968).
The SFPD range where Harry meets the four "rookies" is in reality the Oakland (California) Police Department's indoor range. It's now closed, partly due to the many "Dirty Harry" fans who kept trying to sneak into it, but mostly due to indoor inhaled lead problems.
According to Clint Eastwood biographer Marc Eliot the addition of a black partner Early Smith was a "conscious attempt by Warner to ameliorate the outrage that the punk in the 'Do you feel lucky?' scene (in 'Dirty Harry') was black."
In the film, Carol McCoy hits on Harry after explaining the circumstances behind her divorce from Charlie. She pulls close to kiss Harry when her rambunctious children's play interrupts them both; a phone call from Earlington Smith to Harry (pertaining to the Cost Plus store stakeout) then forces him to cut short their date and extricates him from a clearly awkward situation. However a publicity photo circulated overseas shows Harry and Carol relaxed and kissing - a different version of this scene where Harry succumbs to Carol's advances was reportedly filmed (and which would have changed the dynamic of Harry's relationship with Charlie) but discarded; it was from this discarded scene that the publicity photo came.
Late in the movie when Harry initially makes his partner, Early Smith aware of his suspicion that a rogue death squad is operating within the department, he make casual reference to a similar situation in Brazil that occurred a few year earlier. This is a reference to the infamous Esquadrão da Morte (death squad) that operated in the mid to late 60s during a time of military dictatorship in Brazil. Led by Detective Mariscot Mariel the squad was made up of rogue members of the police and judiciary, and financed by the business community. Their purpose initially was to assassinate known criminals who could not be brought to justice legally but they later carried out political assassinations and general acts of terrorism against the regime's enemies.
As with the first Dirty Harry (1971) movie, Clint Eastwood performs all his own stunts. His face is clearly visible in several stunt sequences which includes him clinging to the hood of Palancio's moving and swerving car, and the climactic motorcycle chase sequence.
Frank Stanley was hired as cinematographer and Lalo Schifrin once again conducted the score and filming commenced in late April 1973. During filming, Clint Eastwood encountered numerous disputes with Ted 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 director of photography Rexford L. 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 air traffic controller who speaks to Lt. Briggs wears a pocket protector which reads "PATCO". This stands for "Professional Air Traffic Controllers Organization" and was the union whose members were fired by Ronald Reagan for going on strike in 1981.
One of two occasions where a Dirty Harry sequel and a western directed by Clint Eastwood (High Plains Drifter) were released the same year, over the summer and winter. In 1976, Eastwood directed and starred in Outlaw Josey Wales, released over the summer, with the third Dirty Harry movie, The Enforcer, released that winter.
As of mid 2015, all of the actors portraying main characters in this film are still living, except for one of the youngest, Robert Urich, who died of cancer in 2002. Tim Matheson is the youngest of the main characters and is one year younger than Urich.
The two escort carriers were the former Rabaul (which was acquired by the navy after World War II, but never commissioned, and never saw service of any kind) and the former U.S.S. Badoeng Strait. (which was completed too late to serve in World War II, but saw action in the Pacific, including combat during the Korean War).
Legendary stuntman, Dar Robinson, did several of the motorcycle stunts, as well as the stunt when 'Davis' rides the motorcycle off the aircraft carrier and into the bay at the end of the 'showdown' between he and Callahan.
In the combat range competition sequence, Harry explains, to one of the rookie cops, that to make his much vaunted .44 Magnum more controllable he uses a "light" .44 Special load, a much less powerful cartridge than the .44 S&W Magnum, while practicing.
This film made Hal Holbrook a recognizable star. When he learned he had been cast in this film he was delighted. He later said that the reason was that, as this was the sequel to the highly popular Dirty Harry (1971), it meant that finally he would be in a movie that people would actually see.
The trivia items below may give away important plot points.
The plot of the film was inspired by the death squads of Brazil that were in the news at the time. John Milius pitched to Clint Eastwood a scenario of Harry Callahan similarly encountering a corrupt police force of vigilantes assassinating those they could not convict. Eastwood liked the idea particularly since he wanted to address the controversy of the original film supposedly endorsing fascism, by making it clear Harry was not a vigilante.
The motorcycles used by the "death squad" cops through most of the movie are Moto Guzzi Eldorado police bikes. However, Triumph 500cc T100 Tiger motorcycles were used during the scenes on the aircraft carrier at the end. These were favoured by the stunt riders as they were lighter and easier to handle than the Moto Guzzis.
Actor Mitchell Ryan plays a character who gets killed during the film. The day his death scene was scheduled to shoot, Ryan was ill. He brought a doctor's note that read Ryan was "too sick to die" that day.
Two deleted scenes help explain why Harry grows to suspect John Davis and his pals with the killings of Charlie McCoy and the mobsters. One occurs between the funeral flight for McCoy and the combat championship; after the flight Harry and Davis drive from the airport to a bowling alley for a few drinks; a black youth is suddenly chased outside and assaulted by four toughs; Davis attacks the toughs while Harry dispatches one with his beer mug. After subduing the robbers Davis harangues a group of eyewitnesses for letting such crimes take place; Harry witnesses Davis' harangue and sees in it his own approach to crime fighting, albeit far more severe. Later, after examining the bullet from Davis' gun at the combat championship range, Harry checks on old issues of a police magazine, in which are articles condemning the revolving door justice allowed by liberal politics - articles authored by the four rookie cops. These scenes were deleted presumably because they were judged to be "padding" and not necessary to establishing Harry's suspicion of the four rookie cops.
On April 22, 1974, two men robbed a Hi-fi shop in Ogden, Utah, made the five hostages drink Drano, and then shot them in the head. The next day an unnamed informant called in a tip to Ogden City Police with information that would help wrap up the case much sooner than police had anticipated. The informant, an airman stationed at Hill Air Force Base, told police that he had overheard two of his fellow airmen talking about robbing a store and killing witnesses utilizing the "Death By Drano" method by which the pimp murders the prostitute in Magnum Force (1973), which the two had seen prior to the crime. Two of the hostages miraculously survived. The crime would forever be known as The Hi-Fi Murders.
Clint Eastwood strongly disagreed with the notion that Det. Harry Callahan was a vigilante, and one of the reasons he made "Magnum Force" was to contrast Harry's inside-the-system, if brutal, approach with the true vigilantism that the rookie cops pursue. Eastwood also pushed successfully to keep the scene that makes this explicit, where Harry tells the vigilante's leader Lt. Briggs that he hates "the system" but will do his job inside of it until it can be fixed.
Even though Lt. Briggs (Hal Holbrook) is dead at the end of this movie, a different character named Captain Briggs played by Bradford Dillman appears in Sudden Impact (1983). Dillman previously played Captain Jerome McKay in The Enforcer (1976). It is unclear whether these two Briggses are related or just have the same last name.