system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How military units get their numbers?  Like where does 25th ID come from?  Wheres 24th ID? 

I dont understand the number structures at all and what they symbolize. I get that there is like a 1st INF DIV but why is their FA unit Charlie 3-07 (just as an example)?
gpt
It's largely random. In WWII we had the first, second, and third armies, but then you get reasons like:

-SEAL Team 6: Actually the second SEAL Team, but we wanted the Russians to think we had more.

-112th Airborne: Made up of 2 different units, something like the 50th and 62nd, couldn't decide whose number to take when they got combined, so they just added them.

Other units were just split up and given "the next number" that wasn't being used and then became autonomous by circumstance, so they were reinforced and became their own unit. Really there's no single rhyme or reason to it.

Charlie 3-07 sounds more like a callsign. Like the 7th crewman in the 3rd vehicle of Charlie platoon.