A slip coach, slip carriage or slip portion in Britain and Ireland, also known as a flying switch in North America, is one or more carriages designed to be uncoupled from the rear of a moving train. The detached portion continued under its own momentum following the main train until slowed by its own guard using the brakes, bringing the slip to a stop, usually at the next station. The coach or coaches were thus said to be slipped from the train without it having to stop. This allowed the train to serve intermediate stations, without unduly delaying the main train. The reverse process defied the ingenuity of inventors.