How do you become a general?

Just asking the question out of curiosity. Starting at the point of a freshly commissioned HPSP/USUHS student, how do you eventually rise up to become a General in the military medical corps? What kind of positions and commands would you apply for as a resident, attending, etc? How long would it take? I've heard that becoming a O6 is pretty much guaranteed if you commit to 20 years, but how about beyond that?
Source: Student Doctor Network - Category: Universities & Medical Training Authors: Source Type: forums