Gun fetishists should warm to this sequel to “The Rise of Cobra,” the dismal 2009 entry that initiated a would-be live-action franchise based on the long-lived Hasbro toy line that in turn spawned numerous comic books and animated TV series. The soldiers who make up the G.I. Joe elite force ooh and ah over their weaponry almost as much as Steven Colbert does over his Sweetums, or the muscle-car fanatics do over their souped-up vehicles in the “Fast & Furious” movies. One scene in particular, in which Bruce Willis, smiling his trademark smug smirk as a retired general, reveals the staggering arsenal he keeps concealed in his suburban house to the younger heroes, should send pulses racing in those who drool—as the task force members do here—over all the assault weapons and other military paraphernalia he has on hand.

But if such gun-show displays leave you cold, “G.I. Joe: Retaliation” will probably do likewise. It’s a cartoonish action spectacle dominated by firefights, explosions and martial-arts combat, all in the service of a story that would be considered dumb even in a low-grade comic book. It starts in the middle of things, with the US President (Jonathan Pryce) somehow having been taken prisoner and replaced by Zartan (Arnold Vosloo), a leader of the malevolent Cobra outfit that’s out to conquer—or destroy—the world. Zartan has been turned into a duplicate of the president through advanced nano-technology.

Cobra’s scheme then continued with the assassination of the Pakistani president. But though the Joes—now led by Channing Tatum’s Duke, with Dwayne Johnson’s Roadblock his right-hand man—foil a terrorist attempt to highjack Pakistan’s nukes, one of their number—the masked Snake Eyes (Ray Park) is fingered as the assassin. Having been captured somehow (like so much of this background, the “how” is never explained), he’s transported to an underground prison where he’s to be kept in stasis alongside the Cobra Commander (Luke Bracey).

But he turned out to be another Cobra agent, the white-masked Storm Shadow (Byung-hun Lee), who engineers the escape of Cobra Commander, though he’s injured in the process. CC joins “President” Zartan and brutal enforcer Firefly (Ray Stevenson) to destroy all their nukes prior to demanding their surrender in the face of the group’s satellite-based doomsday weapon. Meanwhile, Zartan orders an attack on the G.I. Joes—named by him as traitors—which leaves Duke deceased and only Roadblock, pretty Jaye (Adrianne Palicki) and stud Flint (D. J. Cotrona) alive and looking for justice. And the real Snake Eyes (Ray Park), joined by sexy recruit Jinx (Elodie Yung), tracks down Storm Shadow, who’s persuaded to join the good guys when he’s made to realize that his turn to evil as a child—when he was wrongly accused of murdering his martial-arts master—had been engineered by Zartan.

All of this leads to a big confrontation between Cobra and the remaining Joes, of course. Guess who wins. And guess whether the countdown of the doomsday machine will be stopped precisely three seconds before it’s set to go off.

This is utterly silly stuff, played without the saving grace of humor. (The groan-inducing banter between Duke and Roadblock certainly doesn’t qualify, nor do Zartan’s acerbic insults, directed at such easy targets as an unnamed North Korean leader). That’s not to say it isn’t proficiently made—the effects are good, and director Jon M. Chu exhibits the choreographic expertise he perfected in a couple of the “Step Up” movies and a Justin Bieber documentary in the staging of the action sequences, even if the editing by Roger Barton and Jim May renders some of the fights pretty messy. (A battle on cables in a mountain gorge is especially well crafted, though its similarly to scenes in several other movies makes it less effective than it might have been.)

But the acting is strictly comic-book quality throughout—including the supporting turn by Wayne Goggins as a prison warden—with Johnson and Tatum just striking poses and Willis using his “Die Hard” shtick to an irritating degree. Pryce seems to be winking at the material with his over-the-top double turn, but if so it doesn’t work.

“Retaliation” is aimed squarely at the mentality of the target audience of the toys it’s based on—adolescent boys. They’ll probably revel in its pointless—but also bloodless—mayhem, which at one point includes the complete destruction, though from a distant point of view, of London. And they’ll probably swallow its absurdly macho attitude, too. Those of more mature years who share that mentality will probably devour it, too. But everyone else will find it just a bombastically brainless summer behemoth that’s arrived a few months early.