All of the above are a bit off re "seen the elephant."

The version I've seen and heard, at least, holds that mastodon fossils had been found in the unsettled territories "out west" prior to the legal settlement.

The waves of migrants who travelled west to settle were often regaled with stories that implied that the "elephants" - great and dangerous beasts, still roamed in unknown places, and that the settlers might run into one at any time.

Although it was common enough "conventional wisdom" that there were no elephants. "I've seen the elephant" was an often used explanation given by

          THOSE WHO QUIT AND WENT BACK EAST.

Two interpretations for "seen the elephant:"

1. Gave up for unknown/unexplained reasons.

2. Something (that they didn't want to talk about) SCARED THE SHIT OUT OF 'EM.

Settlers who gave up would often be urged by others that they stay, since in those times cooperation and mutual help within the community was very necessary, and the loss of one, or one family, was a threat to all who stayed. "Seen the elephant" was simply an unarguable non-explanation that said the mind was set and argument was useless.

The second probably is the context in which a military person might have used the term in WWII era. Sort of an "I was really scared and I don't want to go back there again." Sometimes (usually?) it carried the notion of "I don't think I CAN go back again." But they usually went back again.

John