On paper, this latest entry in Clint Eastwood’s string of films about American heroes (see “American Sniper” and “Sully”) must have sounded like an interesting experiment—a recreation of the thwarting of a recent terrorist attack in which the true-life protagonists play themselves. In the event, however, despite its potent subject matter “The 15:17 to Paris” proves inconsequential, largely because of the banality of the dialogue, direction that for the most part feels listless and unfocused, and strenuous stabs at acting by the leads that unfortunately fall far short.

The shortcomings begin with the script drawn by Dorothy Blyskal from the non-fiction account of their ordeal by Spencer Stone, Alek Skarlatos and Anthony Sadler (with help from Jeffrey E. Stern), which falls into a number of distinct parts. After an introduction reminiscent of (but greatly inferior to) the start of Hitchcock’s “Strangers on a Train” in its emphasis on waist-down shots of moving feet, we see the men, along with Ayoub El-Khazzani (Ray Corasani), boarding the fateful train on which they will confront each other on August 21, 2015. There will be periodic shots back to this lead-up to the encounter throughout, a tactic that actually undermines suspense rather than stoking it.

Then we flash back to the childhood of the three unruly friends. Spencer (William Jennings) and Alek (Bryce Gheisar) are close pals who stand apart from their classmates at a Sacramento Christian school, not least because of their insistence on wearing camouflage shirts, and are ridden hard by most of the teachers and the principal. Both are living with single moms (Judy Greer and Jenna Fischer, respectively) and seem to have a fixation on military role-playing. (It’s a mite unsettling to find Spencer hoarding a large collection of toy guns, for instance, and having a poster for “Full Metal Jacket” on his wall.)

The buddies link up with another student making regular trips to the principal’s office—cool dude Sadler (Paul-Mikel Williams), who’s soon trading darts with them in mock battles in the California woods. Though they’re separated when Alek moves with his dad to Oregon and Sadler transfers to public school, they remain close friends.

The focus now shifts almost exclusively to Stone, who decides to join the Air Force and goes through rigorous training to make the grade (echoes of “Jacket” again, though the outcome is nowhere near as dire). As both he and Skarlatos, who’s finishing up a tour in Afghanistan with the Oregon National Guard, are approaching leaves, they decide to meet and tour Europe together, and Stone invites Sadler, a Cal State student, to join them.

This leads into a long, rambling section of the picture depicting their visiting Rome, Venice, Berlin and Amsterdam—endless shots of them walking about, meeting locals and other Americans, and taking innumerable selfies, until they board the train to Paris. It’s then that the violence erupts, and they subdue and capture the gunman, in the process saving a passenger who has been shot. The picture closes, in a sequence blending news footage with newly-shot material, with their being awarded honors by French President François Hollande. (He also pins ribbons on a Brit and a couple of Frenchmen, though they receive little attention here.)

The train sequence is easily the best part of “The 15:17 to Paris,” shot largely with a hand-held camera by cinematographer Tom Stern, even if the lead-up to it, in which Ayoub is shown readying himself for the assault, generates surprisingly little tension as staged. The childhood scenes have an odd Afterschool Special feel that even Greer and Fischer can’t penetrate, while the touristy midsection is frankly as boring as watching someone else’s home movies of their trips abroad. Clumsy allusions in the dialogue about Stone’s feeling that a higher power is directing him to some important purpose are especially embarrassing, as are the spare, tinny music cues by Christian Jacob sprinkled throughout.

As for the three young men, they are undoubtedly heroes, deserving of celebration. They are not, however, actors. Sadler, who possesses a natural, loose charm, comes off best, though his background after elementary school is given short shrift. Skarlatos, similarly, gets little background treatment, and doesn’t appear very comfortable on camera.

Neither does Stone, quite frankly, though the burden of carrying the picture is placed on his broad shoulders. He handles the concluding action, as one might expect, convincingly, but his line readings have the frantic tone of an amateur straining desperately to seem convincing. Oddly, a professional actor would probably have brought greater authenticity to Stone than Stone himself does.

The story of Stone, Skarlatos and Sadler is, as Hollande said, an inspiring one that deserved to be told. It’s a story, though, that deserved to be told better than Eastwood manages to do.