Big Jim posted:What are "snappers?"
That is what the good folks on the PRR called a "Pusher". The Brits called them "Bankers". Go figure.
The Brits call them "Bankers" because they assist trains in climbing emBANKments. That's what they call grades over there. That and "inclines" as in the Lickey Incline, the steepest mainline grade in England at "1 in 37.7' or 2.65%.