A Heberlein brake is a continuous railway brake used in Germany that is applied by means of a mechanical cable. Train braking is therefore initiated centrally from the locomotive using a winder. This causes the brake clips to be applied on individual wagons, assisted by a servo system which makes use of the rotation of the axle. The brakes operate automatically if the cable snaps. A typical feature of Heberlein brakes is the clearly visible cable run on top of the wagons, but cables can also be led underneath the wagons, as on the Spreewaldbahn railway line. Heberlein brakes were eventually largely replaced by compressed-air brakes or, sometimes, by vacuum brakes on narrow gauge railway vehicles.