Uh-oh.

Nobody should be surprised — least of all Warner Bros. — that  “Gangster Squad” is a terrible movie. Anyone who saw the trailers or heard the industry gossip knew that it was going to be dreadful. It was a guaranteed disaster before the ink dried on the contracts.

But there’s a greater issue with “Gangster Squad” than its failure. The movie is a betrayal of history. It’s clear that when Susan King of The Times starts a story with the absurd statement “… mobster Mickey Cohen ruled Los Angeles in the late 1940s,” that the past —  and the truth — have been obliterated in the public consciousness. More important, “Gangster Squad” is the betrayal of a rare opportunity to do it right.

It may seem like overkill to perform a detailed autopsy on a forgettable costume picture that isn’t even a good popcorn movie. But as dismal as the movie is, there is a larger lesson to be learned about the evolving genre of Los Angeles on film: “Gangster Squad” is significant if only because it breaks the spell that “Chinatown” has cast over period L.A. movies since it came out in 1974. Noah Cross, with his quiet but all-consuming malevolence, has been pushed aside by the profane pipsqueak Mickey Cohen.

[Spoilers ahead.]

“Gangster Squad” originated as a 2008 series in The Times that was the life’s work of Paul Lieberman, who spent years interviewing members of the LAPD’s Gangster Squad. In full disclosure, I was the copy editor on the series so I worked with Paul closely on the stories (“Crusaders in the Underworld” is mine, by the way). Paul is one of most tenacious people I’ve ever worked with. In fact he went to heroic lengths to interview some of the Gangster Squad members. Paul can be charming but even he would have to admit that he is a tough, unrelenting negotiator and drives a very hard bargain – and I have to wonder how much script approval he fought for along with his producing credit.  Having one’s life’s work turned into a Hollywood fairytale cannot be a pleasant experience and it’s hard to think that Paul simply took the money and walked away as some writers might.

The series unintentionally made the Gangster Squad look like a bunch of fools who spent years clowning around and never accomplished much except getting a key informant killed: Jack “the Enforcer” Whalen. Neither the squad — nor the entire LAPD — ever really laid a glove on Meyer Harris “Mickey” Cohen,  which is why he finally went to prison on a federal charge of income tax evasion.

I didn’t read Paul’s book, published in 2012, because I already had my fill with the series. The Times stories were written in a pseudo-hardboiled tone, which is almost impossible to get right, and I figured that the book would be even worse.

Given the real Gangster Squad’s lack of achievements and colossal blunders (it was involved in the Leslie Dillon debacle in the Black Dahlia case), there wasn’t any material for a movie.  Failure was inevitable.

Sean Penn as Mickey Cohen with a Thompson submachine gun and 100-round drum. Oh that hat.

The filmmakers obviously realized this, because the movie is what we do in Los Angeles with an old house: buy the lot, demolish everything but the front door and call it a remodel;  an overblown McMansion with a 1950s (pardon me, “mid-century”) facade, granite counters and his and hers toilets.

In this case, director Ruben Fleischer tore off the cover and threw the rest of the book in the trash. To add a bit of authenticity, the movie takes a page from the James Ellroy playbook and tosses in the names of some conveniently dead people, such as Jack Dragna, who died of old age in a Hollywood motel in 1956 but in the film is killed by Cohen’s assassins, one of many historical betrayals in “Gangster Squad.”

The fundamental problem with “Gangster Squad” is the fictional script (“inspired by a true story”) by Will Beall, a former LAPD detective who until the release of this movie was sometimes described as “an up and coming writer.”

Beall has gone on the record as saying that he envisioned the movie as a western, and there would be nothing wrong with this, except he’s written a tired, worn-out cowboy movie full of cliches of the 1940s or ‘50s that could be named “Double Cross at Triple-A Ranch” or “Showdown at Comanche Creek” and might be aired on the Buckaroo channel at 2 a.m.

Still, in that moment when Beall decided to write “Gangster Squad” as a western, the iron grip that “Chinatown” has held over the fictional Los Angeles for nearly 40 years was broken.

Photo: The virtually immobile Nick Nolte (right) as Police Chief William Parker, with the wooden, monosyllabic Josh Brolin  as John O’Mara.

Here’s the plot of Beall’s western, stripped of its 1940s facade:

An ailing sheriff (Police Chief William H. Parker/Nick Nolte) deputizes a motley crew of gunslingers, lowlifes and ne’er do wells to drive out the greedy, evil land baron (Mickey Cohen/Sean Penn) under the leadership of a idealistic Civil War veteran (Sgt. John O’Mara/Josh Brolin), who is building a new life in the West with the help of his pioneer-spirited wife (Connie O’Mara/Mireille Enos).

Photo: Grace Faraday (Emma Stone) channeling Jessica Rabbit in “Gangster Squad.”

Bullets fly and bodies fall, leading to an apocalyptic shootout and a final confrontation in which good triumphs over evil. Throw in the fallen woman with the heart of gold (Grace Faraday/Emma Stone), the crooked judge (Judge Carter/John Aylward) and some saloon scenes (re-creations of Slapsy Maxie’s and the Club Alabam) and it’s a wrap.

This is not the makings of a great gangster picture or even a good one. It’s not even the makings of a B western. It’s a movie that those of us of a certain age have seen again and again.

Photo: Max Kennard (Robert Patrick), right, a character who wandered out of the old West and into “Gangster Squad.” He even gets a Latino sidekick (Michael Peña), center. At left, Ryan Gosling.

The most glaring and ridiculous example of the movie’s origins as a western is Officer Max Kennard (Robert Patrick – the T-1000 unit in “Terminator 2”), who looks like he wandered off the set of “Gunfight at the O.K. Corral,” slings a single-action revolver — in 1949 — and  has lines like “This here is fixin’ to be a jailbreak.”

Kennard even gets a Latino sidekick (Navidad Ramirez/Michael Peña), but he’s inept and bumbling rather than funny (like Leo Carrillo) in what I consider a fairly demeaning role. A few lines could have made a real difference with this character.

Photo: Bless you, Anthony Mackie! You’re the only one in “Gangster Squad” who knows how to wear a hat!

The quips like “OK, Hopalong,” by the African American officer (Coleman Harris/Anthony Mackie yes, in the world of “Gangster Squad,” the LAPD of the 1940s embraces racial equality)  only underscore the absurdity.

But there are many other examples, like this dialogue between O’Mara and his wife, Connie, which could have been swiped  from any B western:

(John O’Mara comes home to his pregnant wife. He’s battered and bruised from beating up the bad guys.)

Connie: Baby, you promised me.

O’Mara: I know.

Connie: You stood right where you are standing now and promised me.

O’Mara: I know. I didn’t go looking for it. Scout’s honor.

Connie: John, you go looking for it every time you leave the house.

Or:

(O’Mara tells his wife that he’s organizing a posse to take on Mickey Cohen).

Connie: When we moved out here you said we  found paradise, remember? The wind was right. We saw the ocean right through that window.

O’Mara: That’s exactly what kept me going when  I was over there was raising a family here. You can’t ask me to just hand it all over to Mickey Cohen.

Connie: Mickey Cohen can have L.A. as far as I’m concerned. He’s welcome to the whole lousy town. He just can’t have you. Sweetheart, the war is over. Stop fighting. Come back to me.

O’Mara: I’m tryin’. I need your help.

Photo: Mickey Cohen (Sean Penn) rants about Manifest Destiny to Jack Dragna (Jon Polito). In reality, Dragna died of natural causes in a Hollywood motel in 1956. And in real life, Cohen (Jewish) never worked for Dragna (Sicilian). Never.

Perhaps the best example of a western masquerading as a gangster picture comes in this tirade from Mickey Cohen. Cohen and Dragna are discussing Cohen’s killing of Tony Russo, who is chained between the back bumpers of two cars and pulled in half up by the Hollywood sign. (The credits on imdb, although lengthy, are incomplete. Maybe someone can help me out on the actor playing Russo).

Dragna: What you did to Russo, that was a disgrace, Mickey. Man that rode on a train out from Chicago to sit with you in good faith. I don’t get you. You have the world by the ass out here. You got all the prestige, the person,  the pussy any man could ask for. And you go and poke Chicago in the eye.

Cohen: ….. You can drink to Tommy as a guy who died building the railroad. And I’m sorry he won’t be out here when I drive in the golden spike.  But what happened to Tommy is nothing. That wasn’t murder. It’s progress. I am progress.

Dragna: You know what kills me is you think you’re something new. I’ve seen guys like you before. The Mojave is filled with them. Bright boys that want to shoot their way to the top of the class. They think they got vision. It’s the other way around. Matter of fact, I’m having a vision. Right now. You are going to wake up one morning with your best parts stuffed into your mouth.

Cohen: I’m sorry did you say something? I was kidding. I heard you, Jack. You’re a funny guy. And I’m not going to carry water for you anymore.

Dragna: You dumb kike.

Cohen: You’re old. You’re slow. I’ve outgrown you.

Dragna: I may be getting old. I may be getting old. But I’ve got friends in Chicago that are neither…

Cohen: This isn’t Chicago. This is the wonderful fucking West. I been reading about it. You heard of Manifest Destiny? That’s when you take what you can when you can. The greasers took it from the redskins and we took it from them and I’m going to take it all from you, Jack. And not just because I can, but because this is my destiny. Los Angeles is my fucking destiny.

Mickey Cohen ranting about the golden spike and  Manifest Destiny? Please. This is nothing but a horse opera.

Photo: The old ranger Max Kennard (Robert Patrick) with his single-holster rig.  Seriously. In 1949?

Of course, when “Gangster Squad” gets the cast out of their dusters and Stetsons and into double-breasted suits and fedoras, it needs to mob up the atmosphere, so there are some random bits of boilerplate about setting up a book, running a wire, controlling the heroin market, etc. It’s all window dressing not to be taken seriously.

And except for Kennard, who fans his single-action revolver with movie-perfect accuracy, the rest trade in their six-shooters for heavier artillery. By the end of the movie, everybody has a Thompson submachine gun and the more fortunate ones (like Mickey Cohen) get 100-round drums.

Unless you’re Woody Allen, it’s virtually impossible to make a movie without explosions, car chases and gunfights, so there’s a lot of them: The vintage cars screech and tumble and blow up and more shots are fired in “Gangster Squad” than during the D-day invasion.  It’s slo-mo time during some of these gunfights, and in the final, apocalyptic shootout around a Christmas tree, ornaments disintegrate into fragments and shell casings drop to the marble floor of Mickey Cohen’s temporary fortress (he has rented an entire hotel) in a leisurely ballet of violence.

The cast doesn’t have much to work with in a script like this and nobody really breaks a sweat except for Sean Penn, who does enough acting for everybody else in the picture. Penn channels Cody Jarrett (James Cagney) at the climax of “White Heat” for the entire film, which is just as exhausting as it sounds. But for all his histrionics, Penn’s version of Cohen is never threatening or sinister. More like a loud drunk down at the end of the bar who is spoiling for a fight. (And in the movie, Cohen mostly kills his own men who have screwed up.)

Photo: Ryan Gosling cannot wear a hat.

The fact that I’ve gotten this far before mentioning Ryan Gosling (who plays Jerry Wooters) as the token ladies’ man of the posse ought to tell you something. He’s sort of mumbling eye candy and looks like he wandered in from the set of “The Bachelor.” There is a moment when he encounters O’Mara’s wife, Connie, during a backyard barbecue that implies a certain muted chemistry that I suspect might have been swiped from “Shane” but really serves no purpose in “Gangster Squad” except to reinforce once again the movie’s western roots.

Even farther down the cast list is Giovanni Ribisi as Con Keeler, the rather meek technical wizard who hits on the idea of bugging Cohen’s home. There’s simply nothing to work with in this role.

And then there’s the obviously fragile Nick Nolte. If you pay attention, you’ll notice he is either sitting or standing in all his shots and barely moves.

To be continued…