That term is old and used in a lot of situations. Military and civilian. Good reference, yes, but might not be the whole reason for it.
English
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Thats cool fact, never knew that
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No problem, I use it to describe someone who is troubled or preoccupied. They look right through you, happens in tough situations in the military. Kind of a blank, non-caring stare. First 20min of Saving Private Ryan shows MANY 1000 yard stares.