The Mac Plus is an excellent machine with an excellent design, but pretty as the case may be, it has one fault: it's made of plastic. And plastic simply isn't good enough for the army. The TPI-863, made by Techmatics Technologies, Inc., solved this problem for the military by recasing the Macintosh Plus in a steel case.
This machine was built to meet Tempest standards. "Tempest is a term given to computers that were shielded from electromagnetic energy escaping into the rest of the world. The purpose was to keep someone from being able to read what was being displayed on the screen, which is apparently readable from some distance away. Lots of government computers were rated tempest to protect our national secrets." William Wyatt