Great Western Railway Power and Weight Classification

[1][2] On 1 July 1905 the Great Western Railway (GWR) introduced a system for denoting both the haulage capabilities and the weight restrictions which applied to their various classes of locomotive.

At first these were painted high on the cab side, but during World War II the blackout precautions meant that staff had to be careful using lights at night, so the disc and letter were moved downwards to a position just above the engine number plate, to make them easier to see.

[4] Certain ex-LMS and BR Standard steam locomotives allocated to the Western Region were given GWR style route classification discs,[4] usually without the power class letter.

The letter represents the power of the locomotive, and is approximately proportional to the starting tractive effort, thus:[1] The "Special" classification was not shown on the "King" class,[6] but in the case of no.

[7] Locomotives loaned during World War II were given GWR power class letters, in order to avoid confusion with different systems used by the lending railway.

A preserved GWR 2884 Class steam locomotive, showing the power classification as a black letter "E" on a blue weight classification disc, painted above the numberplate. Between the disc and numberplate may be seen a white letter "X", which affects how the power class is interpreted
A preserved GWR 4500 Class steam locomotive, showing power classification "C" on a yellow route restriction disc, on the upper cab side-sheet
Two Western Region Diesel-hydraulic locomotives; D7072 (left) is a class 35 showing a red route restriction disc; D6343 (right) is a class 22 and has a yellow disc. Both discs are on the cabsides, below the numbers.
An ex-GWR 6800 ( Grange ) class steam locomotive, showing a white "X" below the red route restriction disc, indicating that the normal loads for its power class (D) could be exceeded
A preserved GWR 6000 ( King ) class steam locomotive, showing the double red discs painted above the numberplate denoting the most restrictive weight classification; the power class (Special) is not indicated