Question about killing people?

ive always wanted to join the army, specifically to be a green beret. I know thats what i was made to do and one day I will accomplish that even if it kills me. nothing can stand in my way except for one thing, im a Christian. now, since they are special forces they dont necessarily kill in self defense. like if they have to take out a sentry or something. I read it is grounds for leniency if you kill in self defense but sometimes they do not. would god be angry if I fulfilled my dream?