>That only flies in an email or on a specialized forum.

Counterpoint: It doesn't.

They made a reply to a military member on a thread about military equipment. Googling a few acronyms + "military" would surely lead one to the answer.

It would indeed. But why push the burden onto all the non-specialist readers, who after all come here to both learn and to take part, rather than expand the initialisms the first time they're introduced in a thread?

I'm reminded of an acronym at work: CIM. They come in two variants, CIM-A and CIM-B. I'd been there a year before I finally decided I needed to ask a more senior colleague what they stood for, and he didn't know either. The intention was obvious from the context of their use (although whether -A or -B was more serious wasn't) but most of the people in the weekly meetings discussing Critical Incident Management didn't actually know that was what they were discussing. Nowadays we have a culture that better encourages definition of terms upon first use, and it's less common that someone needs to ask "stupid" questions.

lol I feel like this debate plays out at least weekly in a HN thread about a subculture, specialty, etc.