For sixty-one days and nights, this extreme training replicates the nonstop stress of warfare. Soldiers sleep an average of three hours a night and receive just one meal per day. They train continuously, running missions 20 hours straight in mountains, swamps and dense woodlands. Most lose 20 or more pounds before it's over, and many quit or fail the course along the way. Only one in three make it though.

To become Air Force Pararescue men, students must survive one notoriously difficult milestone called `Extended Training Day'. Only 10 percent survive the cut.

Marines are pushed to the point of unconsciousness in the pool and they wrestle 90-pound packs in the pounding surf of the Pacific. One in three doesn't make the cut.

The US Army's Special Forces Combat Dive Course takes only the best soldiers. Students are tested in severe underwater conditions to prove they have what it takes.

Navy EOD's embark on a five-day, non-stop series of high stress missions. Make the wrong move, allow fatigue or distraction to take over and the entire team fails.

Waiting hours in the worst possible conditions only to get a few seconds to make the right shot; marine snipers are legendary for being the best.