If you want to learn army combatives or do MMA in a different context, and don't want to do full time military service, the National Guard is a great way into that.
The trick is, you need to pick a combat arms MOS, Infantry especially, if you want to get the most opportunities to play. That, or Military Police.
Side note, level 1 combatives teaches the "Gracie Gift" guard pass. Everyone ignores it right after they go to level 2.