I am on orders to a unit at Fort Drum that will be deployed when I arrive. Will I be able to join them or will I in be Rear Detachment?

There are many variables, starting with how long they will have left on their tour, how far into the prep cycle the rear D trainers are, and whether or not they require your grade and skill set. Thank you for your service.

Rear D unless you are on a by name deployment roster prior to arrival

I am in the same boat. I believe it depends on the amount of time left in the rotation and if they are short handed.