One sad byproduct of war is the fact that many soldiers get too little time on earth to be remarkable.
That's the way it was with Lieutenant Jack Hulme, a golden boy of the ordinary sort: a handsome football player from Pawtucket, R.I., who liked to drink and bellow Hank Williams tunes, a gung-ho Marine until he saw the reality of Vietnam. His death in 1969, at 24, wasn't especially heroic; his compound was hit by a mortar attack. It was unremarkable, too, that he left behind a wife and a 5-week-old son he had never seen.
But ''Unknown Soldier," that son's documentary about the quest to learn about his father, draws power from Hulme's unexceptionality. Devoid of special drama, it ends up as a story that applies to many families -- about the forces that draw parents and children together, the way the dead occupy untouched spaces in our lives, like a bump in the bedcovers we never smooth out.
The 90-minute film, which airs on HBO tonight at 6:30, unfolds with no narration. It relies on interviews with family and friends, strangely beautiful stock footage of the military, and still photos of Jack, who usually wears a goofy grin.
We also see John Hulme, now in his 30s, who says he grew up with little curiosity about his dad. Immersed in his mother's Jewish family in New Jersey, he felt a tenuous connection to his father's side, working-class Catholics.
Now, he examines the Hulmeses at length, lingering most on his grandfather Billy -- known as ''Pa" -- who at 90 is tall and beanpole-thin, narcissistic, and cartoonishly patriotic: On Flag Day, he dresses in a boyish sailor's uniform and stands at attention, with a bugle, on his porch.
Pa's pull on his son's life was strong and complex; he instilled a romantic view of war and an unquestioning fealty to the government. Jack was willing to rebel against Pa when he married a Jewish woman. Pa was so upset that he refused to attend the wedding. But no antiwar protests could sway Jack from wanting to serve. On the day he left for Vietnam, Pa was beside him again, and proud.
If Pa has any regrets, he doesn't say; he's a compelling figure, but flat. The film's emotional weight belongs to John's mother, Ellen, who talks with painful clarity about old wounds and travels with her son to the spot where Jack died. She's as articulate now as she was in 1969, when she sent her husband audiotapes describing her longing and love.
''I don't know if I can listen to that," John says, shaken, after hearing one of them. ''It's so between the two of them."
The scenes that John and Ellen share are the film's most moving; at heart, it turns out, this is a mother-son story. As a history, ''Unknown Soldier" leaves a lot of open space, some of it vexing. We never learn how Jack reconciled with Pa after his wedding, whether Ellen found another love. And, despite the film's promise, we don't get to know much about Jack's inner life beyond his childhood and his collision with fear.
But we do see the small ways death affects a family: the way Jack's boyhood bedroom remained untouched for decades, John's gentle awkwardness when he tries to comfort his mother. And in the end, we get a hint at why John may have wanted to finally learn more about his dad -- an ordinary reason that makes perfect sense.
Joanna Weiss can be reached at firstname.lastname@example.org.