Three Dowty Retarders, exploded to show mechanisms, 5 foot/second retarder, 4 and 12 foot/second booster retarders, in display case, British Railways, c1967, fitted to track in marshalling yard and used to speed or slow wagons during marshalling.

Sir George Dowty was an English inventor who had worked in both in the aeronautics industry and as an engineering draughtsman. His "Dowty" retarder was used in rail yards to manage the speed of rail wagons and cars as they are moving down tracks with an incline.

The maximum speed was specified and set into the devices at the point of manufacture - if the cars were travelling above the speed set on the retarder a valve was activiated to increase resistance, which in turn slows the car.