An introduction to a trinity of SF that I always recommend to my military colleagues
  1. Star Ship Troopers -Robert Heinlein
    I first read this when I was at the Air Force Academy. The description of basic training is visceral, drags up the same emotions I remember. I don't agree with the politics, but Heinlein is always best when you don't agree with him. Plus, power armor!
  2. Forever War- Joe Haldeman
    Haldeman is a Vietnam vet, writing in the vein of Vonnegut's Slaughterhouse Five. Writing SF is a way for the authors to process the memories and emotions of their wars. The action is interesting, but the emotion and homecomings are key. Every time you come "home" it becomes more unrecognizable.
  3. Old Man's War- John Scalzi
    I'll let you read this and find out for yourself why it's so good :). Can't be handing out all the answers. The search makes life good.