Rack focusing can indeed be distracting, specially in a war film like this one, when the film has to have a raw feel, almost documentary-like at times. Very much like zooming, Rack focusing has an artificial quality to it that doesn’t fit every style, it has to be builded into the film’s entire narrative and not only used as a vague storytelling tool just for the sake of it.
I noticed this as well the second time I saw the film. I took it to have a symbolic meaning: the war itself had a lack of clarity; everything for the characters was "out of focus."
just look it up on google, mate: "Rack focus is the filmmaking technique of changing the focus of the lens during a continuous shot. When a shot “racks,” it moves the focal plane from one object in the frame to another. Also known as a "focus pull" or "pulling focus," the technique can include small or large changes of focus. The more shallow the depth of the field, the more noticeable the transition between focal planes."
