Jim...perfect ! Thanks.

The military Robust dates back to the pre-SM models, but it's essentially just a field typewriter. The earlier model had an enclosed ribbon cover, which was sensible as it helped to keep things out of the type basket. And the later SM variant was apparently more resistant to corrosion when exposed to the elements. The hard use travel case was its most notable feature. The early wood crate version is what you'd expect to see when loading equipment in a mobile radio shack. There were various iterations of SM-era travel cases. 

Although I'm sure it was meant to satisfy a military requirement, I would argue the importance of having non-reflective surfaces on something like a field typewriter.