http://www.mactropolis.com/apple-news/us-army-making-the-switch-to-apple-computers/
http://www.schneier.com/blog/archives/2008/01/us_army_install.html
http://www.forbes.com/2007/12/20/apple-army-hackers-tech-security-cx_ag_1221army.html
My error, it was not U.S. Army wide as I incorrectly remembered. However it was to enhance security and that was long before Google got the memo.
If the entire Army had switched, we'd still be talking about it now