In the days of the railways when long trains of cargo would be assembled almost ad hoc, it was not practical to hook up brake lines on every wagon. With the need to drop of cargo at many different locations and sometimes in an order requiring some shunting it would not have been practical to disconnect and reconnect brake lines all the time, assuming that this would even be possible across the myriad of different wagon manufacturers of the day. Such trains were referred to as ‘unfitted’.
The logical solution would be to have a dedicated vehicle specifically for the purpose of slowing and stopping the train. A guard would be stationed in the van, often with a small log burner for heat, and would apply strong brakes by means of a wheel internally. When accompanying the locomotive brakes this would bring the train to a controlled stop. On longer, heavier trains there would often be a second brake van immediately after the locomotive to aid the braking force at the front of the train.