I haven't been able to grasp the concept of putting your life on the line for whatever reason people go into the military for. Some people just want to pay their bills, some people believe in their country and some people do it because their parents did it, but that's rough.
Practice your improv more than learn your lines. 'Cause there's no way you'll be able to learn all those lines in a short time. You have to realize what you know and what you don't know - and what you don't know, just come up with three alternate lines or improv that you can put in that spot.
I did this movie with Spike Lee called Sucker Free City, and that would have to be my favorite role by far. It was just so much fun to work with Spike and shoot in San Francisco.