Now in its 17th year, the war in Afghanistan is the longest armed conflict in U.S. history. The new military drama “12 Strong,” whose primary visual draw is U.S. troops on horseback shooting at the Taliban with machine guns, understands the reasons for that intractability.

Helmed by Danish commercial director Nicolai Fuglsig, the Chris Hemsworth vehicle is is often hammy, but also wryly funny, breath-stoppingly tense, and uncommonly intelligent. Its January dump is a disservice to a promising debut feature.

In almost any other situation, it would be inconceivable to think of the U.S. armed forces — the most formidable military in the history of the world — as an underdog. But “12 Strong” takes place in Afghanistan, where rocks, ammo, and complications are in unlimited supply. More specifically, the film chronicles the first troops to enter Afghanistan, about a month after 9/11. Army captain Mitch Nelson (Hemsworth) has at his command 11 soldiers and a plane that can bomb enemy combatants from 30,000 feet. But on the ground, he and his team are technologically outmatched.

Watch Video: Chris Hemsworth Heads to Afghanistan in New '12 Strong' Trailer

Nelson gets the movie treatment: He has a model-beautiful wife (played by Hemsworth’s model wife, Elsa Pataky), hair that remains moussed after weeks in the desert, and eyelashes so long they apparently adequately screen the lower two-thirds of his face from the sun. He promises to return home with all his men alive and to complete a never-been-done mission in three weeks, not the six allotted by his superiors — and we’re meant to take him at his word.

His second in command, Cal Spencer (Michael Shannon), lives on Planet Earth. The day before he deploys to Afghanistan, his angry wife (Allison King, “Thank You for Your Service”) tells him, “I’ll love you when you get back.” His discomfort on the horses the American soldiers need to ride to reach Taliban outposts leads to a slipped spinal disc. The warlord that the U.S. military needs to court, Rashid Dostum (cast standout Navid Negahban, “Homeland”), almost immediately remarks on Spencer’s “killer eyes.”

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It takes a careful balancing act to convincingly fuse blockbuster feel-good-ism and insightful realism. Thanks to screenwriters Ted Tally (“The Silence of the Lambs”) and Peter Craig (co-writer of the final two “Hunger Games” sequels), “12 Strong” offers both cornpone patriotism and vexed skepticism, as well as a genuine sense of camaraderie among the Army soldiers. Trevante Rhodes (“Moonlight”) and the always welcome Michael Peña, who play members of Nelson’s team, leaven the few moments of respite from the near-constant suspense.

Taking a backseat to untrustworthy allies and figuring out the coordinates for aerial bombardment as the main mission tasks, Nelson’s team fight a new kind of war. That making-it-up-as-they-go-along quality adds to the film’s unexpected freshness, especially as the eager guinea pigs eventually head into battle on horses, with the Taliban’s tanks charging at them as enemy rocket launchers whoosh above their heads.

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Such scenes of steroided Americana are grounded by the film’s best asset: an acknowledgement that, while this particular mission to capture a Taliban stronghold may succeed, Afghanistan is too Gordian a knot for outsiders to understand, let alone solve. (That’s why it’s the “graveyard of empires,” tuts Dostum.)

The mental chess game between the intellectual Nelson and the pragmatic Dostum, especially as the Afghan leader tests the Army captain’s willingness to learn, is fascinating to watch. It’s not that the Afghans are inscrutably foreign; they just have their own histories of rivalries and hostilities that few Americans have the curiosity to learn.

That Nelson and his soldiers are absent from the final confrontation with the Taliban leader that they’ve been pursuing feels surprisingly satisfying. It hints at the convolutions — and bloodshed — to come.

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