Instructors for job training in the military?

[Corey]

I am wondering, with all of the jobs (MOS's, Rates, AFSC's) in the military, there must be many instructors for each job no matter what branch, especially with all of the recruits coming in fresh out of basic for job training. So then how do these instructors get picked, and how do THEY know so much about the job, do they have to go to some kind of school to learn how to teach the job or what? thanks for the answers, real ones only