THIS IMAGE, RELEASED by Warner Bros. Entertainment, shows Chris Hemsworth (left) and Thad Luckinbill in a scene from "12 Strong."

In the days and months following the Sept. 11 attacks, a small U.S. Special Forces unit led an offensive against the Taliban and al- Qaida in Afghanistan. They worked in harsh conditions alongside a local warlord and his men, an uneasy alliance at best, and, even with all the technology and money of the U.S. military, executed the successful mission largely on horseback.

The operation — Task Force Dagger — was classified for years and explored later in Doug Stanton’s 2009 book “Horse Soldiers: The Extraordinary Story of a Band of U.S. Soldiers Who Rode to Victory in Afghanistan.”

Films about U.S. military operations in Iraq and Afghanistan have a somewhat dicey track record. They can veer from too sentimental to too macho and bloviating depending on who’s in front of and behind the camera. But “12 Strong” is, while perhaps not the deepest entry, a very solid movie with an engaging story, script and cast led by Thor himself, Chris Hemsworth.

Only slightly camouflaged behind a modern haircut and some manicured stubble, Hemsworth is Capt. Mitch Nelson, who is on leave with his young daughter and wife (played by his real-life spouse Elsa Pataky) but springs into action at the sight of the World Trade Center falling on the news. He raises his hand to assemble a team and get over to Afghanistan as soon as possible.

It’s when the men get to the Middle East that the film becomes truly gripping, thanks to an ominous score, a hair-raising helicopter ride that rivals moments in Kathryn Bigelow’s “Zero Dark Thirty,” and the inherent tension of a mission that, as Nelson puts it, has no playbook. Their task is to meet up with Gen. Abdul Rashid Dostum (an excellent Navid Negahban) who may be equally motivated to fight the Taliban if properly persuaded.

What separates “12 Strong” from the pack, however, is its ability to introduce and stay with a band of brothers worth caring about.

“12 Strong,” a Warner Bros. Pictures release, is rated R by the Motion Picture Association of America for “war violence and language throughout.” Running time: 130 minutes. Two and a half stars out of four.