Second Fellowship

Pretty broad question, but how does this actually work? I am already subspecialty trained and coming up to about 18 months until my ADSO. I'm considering going back for a one-year fellowship in another field of interest, but I have no clue how this actually works in the military system. I assume I have to apply the same year as my ADSO? How do I actually apply?
Source: Student Doctor Network - Category: Universities & Medical Training Authors: Source Type: forums