What does the REAL IT unit of the military use for most of their servers? BTW: That's the Air Force not the Army.
The title of the article I linked to is
The Army mainly uses Windows. As far as security, Army servers do get hacked, but there's no outside network access to most of the servers so security goes up.
However, while the regular Army web site runs on Mac, their biggest public-facing, limited-access web site runs on Solaris. They are very paranoid about having public-facing Windows servers.