When the USS Zumwalt (DDG 1000) puts to sea later this year, it will be different from any other ship in the Navy's fleet in many ways. The $3.5 billon ship is designed for stealth, survivability, and firepower, and it's packed with advanced technology. And at the heart of its operations is a virtual data center powered by off-the-shelf server hardware, various flavors of Linux...
More here: http://arstechnica.com/information-technology/2013/10/the-navys-newest-warship-is-powered-by-linux/