It must have been really easy for cops to tail suspects in the late 1940s without being noticed. Everyone wore a hat and trench coat and was shrouded in a puff of cigarette smoke.

Perhaps the filmmakers responsible for “Gangster Squad” used this disguise when sneaking into theaters and ripping off other, better movies. The plot of their gaudy crime drama is stolen from the 1987 smash “The Untouchables,” along with a dose of retro California style from 1997’s “L.A. Confidential.”

Regrettably, the new film captures none of the entertainment value of the former or the intelligence of the latter. Instead, watching “Gangster Squad” is like being caught in the middle of a mob war between historical inaccuracy and bad taste.

A stiff Josh Brolin portrays Sgt. John O’Mara, a WWII veteran turned cop who isn’t keen on following the rules.

But as his pregnant wife (Mireille Enos) pleads, “I don’t need a hero; I need a husband.”

Unfortunately for her, heroes are in short supply at the LAPD, which looks the other way when it comes to activities of imported mob boss Mickey Cohen, played by a hammy Sean Penn in exaggerated makeup more suited for a “Dick Tracy” villain. Having cornered the racketeering biz, he’s implementing a communications monopoly that would make him untouchable (there’s that word again).

O’Mara gets recruited to “wage guerrilla war” against Cohen by Police Chief Parker (Nick Nolte — who now looks and sounds like a rusty animatronic version of Nick Nolte). So the sergeant handpicks a group of men who can go off the grid, take the law into their own hands and use whatever other cliché to destroy Cohen’s organization. These include ladies’ man Wooters (Ryan Gosling), tech guru Keeler (Giovanni Ribisi), knife expert Harris (Anthony Mackie), sharpshooter Kennard (Robert Patrick) and some other guy (Michael Pena).

Complicating matters is that Wooters is seeing Cohen’s gun moll, Grace (Emma Stone), on the side. It’s only a matter of time before they’re caught.

Also complicating matters is the timing of “Gangster Squad.” The film’s trailer was pulled in July following the Aurora, Colo., massacre because of a scene in which Cohen’s goons mow down theater patrons. The ensuing reshoots postponed the original September release date.

What they didn’t do was curb the preposterous amount of violence in the screenplay by Will Beall (TV’s “Castle”), based on a book by Paul Lieberman. A hotel bloodbath makes the finale of “Django Unchained” look subtle.

O’Mara’s square-jawed face distracts from the fact his head must come to a point underneath that fedora. He is one of the dumbest, most reckless cops yet put onscreen. His lone strategy: charge into the most inapt situations and fire until the bullets run out.

Director Ruben Fleischer — who made the amusing action-comedy “Zombieland” and underappreciated heist flick “30 Minutes or Less” — tries to frame O’Mara’s actions as if they’re noble. In reality, he’s a living first-person shooter game. Take that, Aurora!

O’Mara actually ditches firearms for the film’s climax … so he can pummel Cohen senseless in front of dozens of witnesses after arresting him for murder.

In reality, Cohen politely served four years in prison for tax evasion.

No matter that the filmmakers toy with history, because nothing rings true in this expensive, talent-wasting sham. It’s merely an excuse for good-looking actors (and Nick Nolte) to play dress-up and drive Packards.

When Gosling’s character first spots Grace across the floor of a swanky nightclub, he asks his buddy, “Who’s the tomato?” The star is trying to talk like he’s in an old movie as opposed to delivering the phrase with conviction. He comes across like a high school nerd auditioning for “Guys and Dolls.”

The real answer to his question? “Gangster Squad” is the tomato, as in rotten.

What others are saying

•  Cary Darling, Fort Worth Star-Telegram: “Emotional resonance and any sense of real danger are about as thin as an L.A. snowfall.”

•  Randy Myers, San Jose Mercury News: “Alternates between violent and silly, until it goes so over- the-top we stop caring.”

•  Nick Pinkerton, Village Voice: “ ‘Gangster Squad’ desecrates the symbols of the movies it alleges to homage, in the process making a once-great language banal.”

•  Rex Reed, New York Observer: “Sometimes the two-fisted, assault-weapon adventures of the gangster squad seem more like the daredevil exploits of Superman, but you won’t yawn.”