William Pitsenbarger died on April 11, 1966, in a jungle firefight not far from Saigon. A member of a helicopter rescue team, he elected to stay on the ground and help the unit trapped there.

Pitsenbarger was recommended for the Medal of Honor, but was awarded a lesser decoration instead. That oversight bothered his fellow soldiers enough that they agitated for the next 30 years to get him due recognition.

This little-known story is highlighted in “The Last Full Measure,” a workmanlike but ultimately effective film. Much of the movie is fictionalized, but its message of heroism and perseverance is intact — and it gathers a group of fine actors in potent supporting roles.

The film opens in 1999, with a Pentagon careerist named Scott Huffman who would prefer to ignore the Medal of Honor petition from Pitsenbarger’s old Air Force buddy (William Hurt). Huffman is played by Sebastian Stan, the sad sack who always brings down the party as the Winter Soldier in the Marvel movies.

This is good casting, because we don’t especially like Huffman, at least for a while. His D.C. mentor (Bradley Whitford, late of “Get Out”) tells him to ditch the case, but when Huffman meets with Pitsenbarger’s devoted parents (Christopher Plummer and Diane Ladd), he gradually gets into it.

Vietnam flashbacks are strewn throughout the movie, a tactic that has mixed results. It’s hard to track what Pitsenbarger is actually doing during the battle, and the action tends to be repetitive.

More successful are Huffman’s meetings with the men who survived the battle. They’re played by Samuel L. Jackson, Ed Harris, Peter Fonda and John Savage (he’s the damaged soul from “The Deer Hunter,” here playing a veteran so haunted by Vietnam that he’s returned to live there).

That’s a pretty impressive cast. And they’re not phoning it in; we see strong work from this group, with Hurt gradually revealing the extent of his character’s damage, and Harris doing his usual precise job of exploring grief and trauma.

Most memorable of all is Fonda, who died last year. His character is especially shell-shocked, and comes out of his house only at night. Amy Madigan plays his fiercely protective wife, who keeps Huffman at bay until after dark.

Writer-director Todd Robinson doesn’t do anything fancy, and at first the film comes on with all the distinction of a TV commercial. A few good lines raise the movie above its formula, as when Huffman consoles a veteran for feeling survivor’s guilt: “Surviving isn’t a crime,” Huffman says. “No, it ain’t,” comes the response. “It’s a life sentence.”

The movie isn’t interested in the big picture, and (beyond puzzling hints about an official cover-up), it doesn’t go into reasons for the war itself. The point here is to highlight a piece of presumed military injustice, and as far as it goes, the case is convincingly made.

“The Last Full Measure” (2½ stars)

Although fictionalized, this is a true story about the effort to get a Medal of Honor for William Pitsenbarger, who died in battle in Vietnam in 1966. The movie is workmanlike, but a strong supporting cast (including William Hurt, Ed Harris and Peter Fonda) makes it effective.

Rating: R, for language, violence

Opening Friday: Alderwood Mall, Everett Stadium, Meridian, Thornton Place, Cascade Mall