Bank engine

Helpers/bankers were most widely used during the age of steam, especially in the American West, where significant grades are common and trains are long.

Careful coordination was required between engine crews to assure that all locomotives were operated in a consistent manner.

Standard whistle signals were employed to tell the helper crew when to apply power, drift or brake.

In the UK, an engine that was temporarily attached to the front of a train to assist with the ascent of an incline was called a pilot locomotive.

The narrow gauge portions of the Denver and Rio Grande Western Railroad, in particular, used "swing helpers", which meant the helper locomotives were placed mid-train at a point where they were pushing and pulling an approximately equal amount of tonnage, said location being referred to as the train's "swing point".

However, this arrangement requires splitting the train in order to add or remove the helper engine(s), which can be a time-consuming maneuver.

To be able to add and remove helper locomotives quickly, which is especially important in Europe due to the high traffic density, they are usually added to the end of the train.

In the UK it was a usual practice for banking locomotives to follow and buffer-up to a slow-moving assisted freight train without coupling (as demonstrated in archive films of banking on the Lickey Incline) before applying more power, thus precluding the need for a standing start.

This procedure is not performed in North America, as it would violate Canadian and United States safety regulations.