According to freethinkers cited in this article from MSNBC, the old adage is

a denial of our contributions,” says Master Sgt. Kathleen Johnson, who founded the Military Association of Atheists and Freethinkers and who will be deployed to Iraq this fall. “A lot of people manage to serve without having to call on a higher power.

A soldier quoted in the article stated that many in the military “wouldn’t tolerate atheism in their ranks.”

According to Belief.net, “non-believers are a growing segment of the U.S. population — some estimate as high as 14%.”