Hall said he met some atheists who suggested he read the Bible again. After doing so, he said he had so many unanswered questions that he decided to become an atheist.

His sudden lack of faith, he said, cost him his military career and put his life at risk. Hall said his life was threatened by other troops and the military assigned a full-time bodyguard to protect him out of fear for his safety.

In March, Hall filed a federal lawsuit against the U.S. Department of Defense and Secretary of Defense Robert Gates, among others. In the suit, Hall claims his rights to religious freedom under the First Amendment were violated and suggests that the United States military has become a Christian organization.

"I think it's utterly and totally wrong. Unconstitutional," Hall said.

Hall said there is a pattern of discrimination against non-Christians in the military.

Two years ago on Thanksgiving Day, after refusing to pray at his table, Hall said he was told to go sit somewhere else. In another incident, when he was nearly killed during an attack on his Humvee, he said another soldier asked him, "Do you believe in Jesus now?"

...He also said he missed out on promotions because he is an atheist.

"I was told because I can't put my personal beliefs aside and pray with troops I wouldn't make a good leader," Hall said.