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Great Western Railway class 455 “Metropolitan Tanks”
Great Britain | 1868 | 140 produced
Original variant on a photo of around 1875
Original variant on a photo of around 1875
Locomotive Magazine, March 1906

For the Metropolitan and District Lines in London, Joseph Armstrong designed the Class 355, also known as “Metropolitan Tanks” or simply “Metro Tanks”. It was created with a driving wheel diameter of just five feet to ensure adequate acceleration. Since the underground tunnels were also to be run through, many locomotives were fitted with a condensation device. No driver's cab was installed, as Armstrong believed it would have reduced staff attention.

With enlarged water tanks and leading axle in outside frame
With enlarged water tanks and leading axle in outside frame
Locmotive Magazine, March 1903

The first 60 machines were built between 1868 and 1878 in three series of 20 units each. In the first two series, all axles were mounted in the inside frame, in the third series the leading axle was in external bearings and the wheelbase of the coupled axles was slightly larger. In the early years, the locomotives were also required to haul goods trains within London city limits until the Class 633 became available. After Armstrong's death, a total of seven more series with a total of 80 more locomotives were procured by William Dean between 1878 and 1899. These had a larger boiler and larger supplies.

No. 3593 rebuilt as 2-4-2T
No. 3593 rebuilt as 2-4-2T
Locmotive Magazine, December 1905

In the 1880s, the first series were already being rebuilt with a larger boiler and larger water tanks. Half and fully enclosed driver's cabs were retrofitted in later years. The first of the older machines were already retired around 1900. However, the newer ones in particular were used for a longer period of time.

With the electrification of the Metropolitan and District Lines in 1905 and 1907, the locomotives were also used on other lines. For this purpose, the condensation devices were removed and partially a push-pull train control was installed. For the routes of the underground, the GWR kept about 50 machines available until about 1930, which were then replaced by the class 6100 Large Prairies. Other locomotives were used in more rural regions and some were even used on the main line. In the thirties most were retired. A total of ten were still in existence when British Railways was founded in 1948, but these disappeared by 1949.

VariantArmstrong 1869Dean 1881
General
Built1868-18781881-1899
ManufacturerSwindon
Axle config2-4-0WT (Porter) 
Gauge4 ft 8 1/2 in (Standard gauge)
Dimensions and Weights
Wheelbase15 ft 3 in
Fixed wheelbase8 ft
Service weight74,368 lbs88,704 lbs
Adhesive weight62,720 lbs
Axle load31,360 lbs
Water capacity1,139 us gal1,321 us gal
Fuel capacitycoal4,480 lbs (coal)
Power
Power sourcesteam
Estimated power400 hp (298 kW)500 hp (373 kW)
Optimal speed21 mph24 mph
Starting effort12,186 lbf13,056 lbf
Power Plant
Driver diameter60 in
Boiler pressure140 psi150 psi
Expansion typesimple
Cylinderstwo, 16 x 24 in
Boiler
Grate area15.8 sq ft16.4 sq ft
Firebox area87 sq ft99 sq ft
Tube heating area999 sq ft1,209 sq ft
Evaporative heating area1,086 sq ft1,308 sq ft
Total heating area1,086 sq ft1,308 sq ft
Calculated Values
steam locomotive
passenger
suburban
condensator
Joseph Armstrong
William Dean
last changed: 02/2023
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