According to "Ruff n Tuff Linux Tablet for Military" (SiliconIndia, 7 February 2012). the Trimble Yuma rugged tablet computer is avialable with Ubuntu Linux installed. The unit normally comes with Windows 7, but it has only a low power Intel Atom 1.6 GHz processor, Linux might be a better option. The unit is IP67 rated for water resistance and has a 7" sunlight readable touchscreen. These types of units are used for surveying, field repair, emergency management and military applications.
There are other rugged tablet computers and cases available, but these do not necessarily meet military standards.