America's most secret Special Forces unit does not even have a name. Formed as the 'Intelligence Support Activity', it has had a succession of innocuous titles to hide its ferocious purpose. It exists to 'undertake activities only when other intelligence or operational support elements are unavailable or inappropriate'. Translated from Pentagon-speak, this means operating undercover in the world's most dangerous places, penetrating enemy organizations including Al Qa'eda, Hamas and Islamic Jihad. 'The Activity' combines the spy work of the CIA with the commando/SAS role of the Green Berets. It not only provides the intelligence on the ground - it translates it into 'direct action'. This is the unit that located Saddam Hussein, and recently led the intelligence operation that found and killed Osama Bin Laden. This is the untold story behind the world's most secret Special Operations organisation.