Handbook of Military Knowledge For Commanders
One of the biggest treats I’ve read is the translated 1980s Chinese document called the “Handbook of Military Knowledge For Commanders”. Exactly as it implies, the document is a hundreds of pages long and highly deep look into the Cold War’s least advanced and most secretive major army. Because of this, it’s an excellent resource not just for the Cold War PLA, but also many of the client states/units equipped, trained, or even just inspired by it. As well for less-advanced (compared to major powers) armies in general.
A lot of this contains basic stuff that any field manual reader won’t find surprising. The layout, at least of the translated version, leaves something to be desired. And there are a few translation quirks like keeping the romanized Chinese word “Fendui”, instead of just saying “units” or “subunits” (as would be appropriate for the context.) In fact, the document has the worst of both worlds in that it shows “Fendui” but not the original characters, making it confusing for both English and Mandarin native speakers.
Still, this is an excellent study of not just that specific army at that point in time (mid-1980s), but also of many principles applicable to all forces at any time. If you have the time to dig through four hundred pages of field manualese, it’s well worth your while.