One day in the early 1960s, 10 soldiers boarded a plane at Fort Hunter Liggett military base in California on what they thought was a routine training mission. The plane climbed into the clear blue sky, levelled out at around 5000 feet and cruised for a few minutes before suddenly lurching to one side as a propeller failed.
In such a situation, it would have been natural for the soldiers to feel fear or even terror. But there was no need. Though they didn't know it, they were in no danger. They were unwitting subjects in a study designed by the United States Army Leadership Human Research Unit near Monterey, California. Its purpose was to examine behavioural degradation under psychological stress - specifically, the stress of imminent death.
Having created a fear-arousing situation, the researchers next introduced a task to measure the soldiers' performance under pressure. The task was something most people find difficult under normal circumstances: filling out insurance forms.
Eventually the last soldier completed his form, and they all steeled themselves for the crash. At that point the pilot turned the plane around - "Just kidding about that emergency, folks!" - and landed safely at the airfield.
Not surprisingly, anticipating a crash landing did interfere with the ability to accurately complete an insurance form. The soldiers in the plane made a significantly larger number of mistakes than did a control group on the ground.
Quite what the soldiers thought about their ordeal we don't know, but one of them did find a way to get even. When the plane next took off carrying a new group of subjects to terrify, the researchers discovered their experiment had been ruined - the earlier group had blown their cover by writing a warning message on his airsick bag.
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