Selection for the SAS is one of the world's toughest job interviews and physical fitness is only the starting point. What's really being tested is psychological resilience and character as candidates undergo sleep deprivation, interrogation and a series of increasingly complex mind games. In this programme, five ex-special forces soldiers re-create tasks from the SAS's secret selection process, putting 30 civilian men through the ultimate test of their physical and - more importantly - their psychological resilience.