I was talking to my supervisor about re-classing today, and something very interesting come out of this conversation. (History) I am currently serving as a active duty CBRN NCO, in a Trans Company. I enlisted in the Army Reserves as CBRN. I re-classed to 31B, when I went to the National Guard. Now I am being told that technically that my primary MOS is 31B Military Police. I was wondering what that means for re-enlistment and promotions. Also, if any can give me a reference for explanation of primary or secondary. Thank you.