“Ah, another ultra-nationalistic war movie I don’t want to see”, my inner skeptic groaned when I first saw the trailer for Mel Gibson’s “Hacksaw Ridge.” The last thing I wanted from a director recovering from racist inclinations was a war film served on a red, white and blue platter.

Thankfully I enjoy being proven wrong by movies that I initially doubt. On the flip side, Gibson’s latest didn’t start proving me wrong until the last act of the movie. The first two thirds of “Hacksaw Ridge” is a preachy mishmash of every other war film; the last third’s saving grace is Andrew Garfield as the soldiers’ saving grace.

“Hacksaw Ridge” tells the true story of Desmond Doss, a dedicated Seventh-day Adventist Christian who decides that it’s his civic duty to serve his country (that’d be the land o’ the free) during World War II. This proves slightly problematic, as Seventh-day Adventists are traditionally pacifists and adherents of anti-violence who tend to not murder people in droves during wartime. His mission to become an army medic that won’t touch a gun severely pisses off the rest of his unit, as conscientious objection wasn’t all the rage among soldiers who had already volunteered to fight.

But Doss is an honored historical figure for a reason. His refusal to take life while he risked his own to save many others is quite a heroic story, and one worth telling cinematically. “Hacksaw Ridge” takes a little while to do so, though. It is a story of three parts: the conventional, the brutal and the incredible.

The conventional portion of “Hacksaw Ridge” actually takes up more than half of the movie. The majority of the film follows Doss’ journey before he ever sees combat. This could be an opportunity for deep character study, but instead we get a steady flow of boring war movie tropes: main man and one-dimensional pretty woman fall in love immediately so that he can have a ‘girl back home’ to show to his brothers in arms, there’s a hardened but comical Army Sergeant yelling one-liners (here it’s the version of Vince Vaughn that watched Full Metal Jacket to prepare), at soldiers nicknamed by their defining characteristics while they train and bond and fight.

There’s a bit of courtroom drama concerning Doss’ objection, but the first hour or so of “Hacksaw Ridge” is largely a string of “seen it all before” that never finds a memorable tone. The screenplay was written by a couple of cinema veterans who may have walked these steps a few too many times.

Once the World War II battles begin, “Hacksaw Ridge” makes a transition to the brutal and begins earning our attention. This movie never once glorifies war: the Battle of Okinawa is painted by shockingly frank violence and the hardened sound design of loud weaponry tearing through human flesh. This will turn some viewers off but excite genre fans: “Hacksaw Ridge” makes the opening scenes of “Saving Private Ryan” look like a wedding reception. This war is hell, not entertainment.

By the third or fourth slow motion shot of a soldier on fire, I got the sense that Gibson was teetering too close to relishing the cruelty (à la his Passion of the Christ), but for the most part this film is as anti-war as its protagonist.

Speaking of — once Andrew Garfield’s Doss gets to saving lives, “Hacksaw Ridge” finally morphs into an inspiring triumph. The last thirty minutes are cheer-worthy: Garfield exudes integrity and dedication as his faith continually leads him back into the fray to rescue his comrades. Surround this performance with a swelling soundtrack, brisk pacing, and emotionally resonant visual images? You’ve got a finale that almost redeems the rest of the movie.

“Hacksaw Ridge” does get a little heavy-handed with the Christian sermonizing, which will either please or deter you depending on your religious bent. But it’s necessary to accurately tell the story of Desmond Doss, and it elevates (the last part of) the film to the realm of poignant spectacle.

★★★ (3 out of 5)