FWIW, the KC-135 Stratotanker first flew in 1956, and entered Air Force service in 1957. >Barry >Seems to me it had something to do with the length of the air >refueling boom out the back of a KC-135 tanker. I don't know where I >heard that. It's the only piece of info I ever came across in regard to >the expression. Good luck with your quest.