First, let me thank you and all those who are serving (or have served) in our armed forces for your courage and your commitment to our nation's freedom. Your task is difficult, but without you our world would be a much more dangerous place?
I too have puzzled over why some people want nothing to do with God, even when facing great danger or death. It's not logical, of course, because whether we die tomorrow or 50 years from now, some day we each will enter eternity and stand before God. Doesn't it make sense, therefore, to prepare for that day now, instead of waiting until it's too late? The Bible is blunt: "Prepare to meet your God" (Amos 4:12).
Most people, I find, who reject God do so for one of two reasons (or for both reasons). The first reason is pride; they don't want to admit that they are weak and need God. This can be especially true of people who are naturally strong and independent. The second reason is a stubborn will; they want to run their own lives, instead of yielding their lives to Christ's control.
Pray for your buddies who don't want anything to do with God that He will open their eyes and help them face their need for Christ. And make sure of your own commitment to Jesus Christ, and learn to walk with Him every day.