Father, Soldier, Son, Netflix review: is joining the military worth the stress?

• Dirs: Catrin Einhorn, Leslye Davis. 15 cert, 99 min

In most documentaries, we catch the drift early on: the shape and message of the film pre-announce themselves. This scenario is impossible with Father, Soldier, Son, a portrait of an American military family which two journalists from the New York Times, Catrin Einhorn and Leslye Davis, began shooting in 2010. Lives change over any decade: there’s no way of guessing where this film will lead us, and the patterns of storytelling we may be used to – typical arcs of political awakening, say – can’t be taken for granted.

Sergeant First Class Brian Eisch is returning from a tour in Afghanistan as the film starts, and we’re shown his tearful reunion with his two young sons – 12-year-old Isaac and 7-year-old Joey – whom he has been raising as a single divorcé. During his six-month deployments, the boys are entrusted to other family members, but these absences weigh on them dreadfully. It’s hard for them to let Brian go on the next tour, and when he returns with a serious leg wound sustained in machine-gun fire, Isaac admits to a degree of relief that Dad’s back and not going anywhere.

Four years later, the leg hasn’t healed, and the lower half must be amputated. This is as far along in the Eisch family saga as factual spoilers might be permitted, beyond the addition of a new mom into their midst – Brian’s girlfriend Maria, who has older children who’ve left the nest, and one of Joey’s age. The focus is equally on the challenges of Brian’s disability, the steep slope to feeling in charge of his life again, and the effects of his ordeal on the boys’ psychology, which is the material that fascinates most.

Isaac, at 16, has poured his energies into aiding his dad, but can’t really imagine pursuing the same career path. He wants kids of his own one day, and doesn’t want them to suffer the same childhoods: you can tell he ponders whether the family’s sacrifice has truly been worth it, a thought that even troubles Brian on darker days of introspection. Isaac vows to go to college, if his grades are good enough, and then enrol in the police force, thereby breaking from a four-generation-strong Eisch tradition of military service.

Without openly opposing him, Brian can’t see it happening. And in Joey he has a plucky miniature cadet in the making, whose patriotism is only increased by the desire to avenge his dad’s injury. He’s a small kid – overpowered easily on the wrestling mat – whose desperation to measure up feels touchingly immature.

The filmmakers ably illustrate how the baton gets passed down: Brian and Joey are gamers who love blowing things to bits. A movie outing to Clint Eastwood’s American Sniper (2014) catches them cooing at the big toys on screen. But Isaac sits apart, more quietly, and you can sense that film’s underestimated backwash of doubt and disillusionment lapping away at him.

There are gruelling twists awaiting the Eisches, and some terrific shot-making, like the sight of one young recruit trapped in formation, his eyes flicking uneasily off-camera, as if the tug of an ineluctable legacy had roped him into submission.

In its outcomes and politics, this film is almost begging to be oversimplified, but it’s well worth staying on the alert for the ironies, the complexities and the tacit questions it finds a host of ways to express. It never hammers us with statements, even if the emotional payload is huge, and we’re always wondering what wake-up-call it might take – for a certain breed of bullish hereditary machismo to falter, slip and mutate between the generations.

Father, Soldier, Son is on Netflix from Friday 17 July