By the end of 1999, America's prison population approached 1.3 million. The job of housing and controlling this huge and sometimes violent captive population has fallen to corrections officers, or "COs". In the last five years, 13 corrections officers have been killed in the line of duty and more than 14,000 are assaulted annually. In this episode, we'll go inside some of America's maximum security prisons, and learn about this dangerous job from those who risk their lives to ‘walk the beat’.