I heard about this around the time they started filming and immediately went to look up the character it's based on, Desmond Doss. I was just as fascinated with him as Mel Gibson (the director of this movie) was. Doss was a Seventh Day Adventist, and a conscientious objector during the Second World War. Despite which, he joined up with the American military because he believed their cause was right. He refused to carry a gun and went into the medics. He dragged something on the order of 75 men out of an active battlefield, an act of bravery so great he was given the Medal of Honor.
Andrew Garfield plays Doss. We see him from an early age, including his often difficult relationship with his father (well played by Hugo Weaving), a First World War vet with (as yet unnamed) PTSD. The movie is somewhat hagiographic, but they do manage to put a human face on the man. Gibson said in the attached "Making of" movie that he was trying to make a movie about faith rather than religion - a fine line to walk, but one he seems to have pulled off. The movie doesn't preach, it just shows Doss in action. The battlefield is brutally bloody and nasty, with people blowing up and entrails all over ... and Doss just keeps wading back in to rescue "just one more." It's ironic to hear in the "Making of" that Gibson actually backed off on the reality (Doss's life is very well documented, despite his being a very retiring man): he was afraid that some of the things Doss did were so over-the-top that people wouldn't have believed it. I had read about Doss finally being injured: when they put Doss's stretcher down beside another injured man, Doss got himself out of the stretcher and put the other guy in because he knew this guy was more in need of help. Gibson deliberately passed on that - and I'm inclined to think it was a good decision. But ironic, when Hollywood is so known for its love of over-the-top gestures.
Another irony is to be found in the form of the nationalities of all the "Americans." The majority of them are Australian (Weaving, Sam Worthington, Luke Bracey, Teresa Palmer), and the main star (Garfield) is British. Vince Vaughn is the only major character who is actually American. And Gibson himself ... used to be Australian. I was 15 minutes into the "Making of" before I realized that Gibson shouldn't sound flatly American. Apparently he talks that way all the time now.
A very good movie. Not for those who are uncomfortable with bloodshed, but at least it's mostly a war movie about the heroism of saving lives rather than taking them.