Gibson, 61, tells the story of Desmond Doss, a religious man who enlisted in the army voluntarily as a medic, even though he had no intention of firing a shot.
In the final days of the ferorcious battle for the Japanese island of Okinawa in 1945, Doss single-handedly saved 75 men under fire without a gun.
In the movie, Andrew Garfield plays Doss, who was awarded the Congressional Medal of Honor from President Harry Truman in October 1945.
What touched you most about the story?
In a cinematic landscape overrun with fictional "superheroes", I thought it was time to celebrate a real one.
I don't see it as a war film, I see it as a love story, and not a romantic love story. About the love that a person has, wanting to never harm his brother.
In the hell of war, when most men descend to the levels of an animal, this guy hones his own level of spirituality, and is able to display love.
This guy is so transcendent to what was going on around him and was so heroic in his need to save life right in the place where it was being taken.
People are calling this your comeback. What do you say about that?
I don't feel like it's some kind of comeback. It's the first time I have stepped back into the saddle as a director in a while, and it's kind of like riding a bike.
But I had been busy writing and developing stuff.
Traditionally, people have not been too willing to back the things that I wanted to generate from myself, so I used to put my hand in my pocket and in that way, they worked.
Nothing has happened for a long time because I wasn't willing to take the risk, because you can get burned too. Of course, I dabbled in acting here and there (laughs), so it was not all bad.
I also got a chance to perfect my fly-fishing technique (laughs), be a hands-on dad and work on myself.
What were the challenges of shooting?
You are not doing medieval battle where it's man versus man with blunt objects. You are doing explosions and bullets and stuff like that. It's all a little more technically demanding.
Camera angles have to be different for that kind of stuff. We were going as fast as we could with a budget that was about 20 per cent less than what I had on Braveheart (1995) ,which was also shot in about half the time.
Do you miss the times you were one of the most sought-after actors?
What I do is seek to fulfil my creative life. And I have the rest of my life - kids, romantic stuff - it seems to be in pretty good order. Those other celebrity concerns, I think they faded far away and even at the time, they weren't what they were cracked up to be. So I am just jaded (laughs).