Man who died in firefight was on 10th tour of duty . Al Qaeda-linked group has expanded its network of fighters . Special ops forces tend to do more tours than other divisions . The U.S. military is facing a new threat from the Islamic State group.
Man who died in firefight was on 10th tour of duty . Al Qaeda-linked group has expanded its network of fighters . Special ops forces tend to do more tours than other divisions . U.S. remains tight-lipped about special ops .