It’s actually kind of neat. They have their own “state” codes for the Air Force or Navy, and that’s how the mail is handed over to the military. They do have to give an apo or the like, but the deployed know that before leaving so family knows how to write.
It gets murkier once it’s inside how they route the mail, don’t know for sure, but as long as you follow USPS guidelines it’ll get to them. So, part of your answer at least