There isn't a broad sweeping answer to this one; it must be decided on an individual basis. Some of Christianity has decided that killing another human is
never justified. The American patriots and the Confederate soldiers all decided that it was more righteous to defeat an enemy for the greater good.
Generally and historically speaking, "Christian" thought on the topic hasn't been recorded by Holy-Ghost-Filled believers with the revelation of the oneness.
The articles of faith of the UPC state (paraphrasing) that UPC members should be patriotic, support and serve in the military in non-combatant roles, so long as the government and/or the military do not ask them to violate their conscience.
I would tell the guy he needs to pray about it, and that the prevailing apostolic notion toward military service is to avoid combat roles.
All men are born with a spark of the voice of God within them. We call this our conscience. Heathen peoples will be judged by their works according to their conscience. People who are considered 'hard-hearted' are people who have learned or been trained to no longer hear the voice of their conscience. The Law was written for such people, and the Law, the conscience, and the words of Jesus himself all agree in their goal: We don't call this the "Golden Rule" for nothing.
The Apostle Paul addressed this when he said that the pagans had the Law written in their hearts:
Threaded Mode
