Data Security is serious business, and in a war zone that can mean the difference between success and failure. Just being in the same room, or even just close. Sometimes just with line of sight, it's possible to gain access to the information that a computer is holding. With sensitive RF sniffers and such, much like War Driving, looking for open wireless networks. Commercial Off The Shelf computers are sieves. They leak RF all over the place. Think of a COTS computer as the Titanic, and then the TEMPEST one would be the one that was truly unsinkable. In a war zone OPSEC is #1. The NSA and DoD require products used in many environments to be secure, to be ETPL certified. That means they're on the Endorsed Tempest Products List. You don't want Tiny ElectroMagnetic Particles Emitting Secret Things!