I was a marine there, assuming the system is still the same, new hires only come in at the gs11 level as a tower only, there are 3 gs11’s and about 18 gs12’s, and 3 gs13 sups.
When a 12 spot opens, the senior 11 moves in and they hire a new 11. So if you see a 12 spot opened up, it ain’t for you.
Edit: if you ask me they should just have 21 gs12 spots and no gs11 spots, it’s a waste to have tower only controllers for the civilians there.