Why was Won Bin forcibly drafted in "Taegukgi: The Brotherhood"?

If they wanted to minimize the number of people going to the military, it seemed like Jang Dong-gun alone would have been enough, but did both Jang Dong-gun and Won Bin end up going?
At the time, Jang Dong-gun tried his best to send Won Bin home, but he wasn't allowed to go at all..