I was using an IBM "proportional type" typewriter in an office in the '70's. I published newsletters and training material.
The problem I see here is that few commander's ever used typewriters. In the mid-70s when I joined...there wasn't a single officer in the squadron who could type. This was all left to the enlisted guys to do, or else the officer had his wife type up the document at the house.
I find that the phrase "proportional spacing" is used only with the wheel typewriters that came out AFTER the Selectric I and II. Later Selectric models had "selective spacing" - it looks more and more as if this could be blown open.
Were you in the Tx national Guard?
My mom typed my college papers for me at her work on an IBM typewritter ... that was in 1979 ... so I know they were in existence at least in the late 70s ...
"I was using an IBM "proportional type" typewriter in an office in the '70's. I published newsletters and training material."
Yup. They were pretty popular back then. Lots of companies used them to punch up their publications and make them look like they were printed.
Do you recall whether it could superscript the "th" (make the "th" smaller and higher than the base type) in something like "111th"?