A
bank engine (
United Kingdom/
Australia) (colloquially a
banker) or
helper engine or
pusher engine (
North America) is a
railway locomotive that temporarily assists a
train that requires additional power or
traction to climb a
gradient (or
bank). Helpers/bankers are most commonly found in mountain divisions (called "helper districts" in the U.S.), where the
ruling grade may demand the use of substantially greater motive power than that required for other grades within the division.