LNER Class A3

LNER Gresley Classes A1 and A3

Class A1 4474 Victor Wild on the turntable at Kings Cross Station Yard (York Road platform in the background).

Type and origin Power type Steam Designer Nigel Gresley Builder Doncaster Works (59) North British Locomotive Co. (20) Build date 1922–1935 Total produced A1: 52 A3: 51 rebuilt + 27 new

Specifications Configuration 4-6-2 UIC class 2′C1 h3 Gauge 4 ft 8 1⁄2 in (1,435 mm) standard gauge Leading dia. 3 ft 2 in (0.965 m) Driver dia. 6 ft 8 in (2.032 m) Trailing dia. 3 ft 8 in (1.118 m) Wheelbase 60 ft 10.6 in (18.56 m) Length 70 ft 5 in (21.46 m) Axle load A1: 20 long tons (20.3 t; 22.4 short tons) A3: 22.05 long tons (22.4 t; 24.7 short tons) Adhesive weight A1: 60 long tons (61.0 t; 67.2 short tons) Loco weight A1: 91.35 long tons (92.82 t; 102.31 short tons) Fuel type Coal Fuel capacity 8 long tons (8.1 t; 9.0 short tons) Water cap 5,000 imp gal (22,700 L; 6,000 US gal) Firebox:  • Firegrate area 41.25 sq ft (3.832 m2) Boiler pressure A1: 180 psi (1.24 MPa) A3: 220 psi (1.52 MPa) Heating surface:  • Tubes A1: 1,880 sq ft (175 m2) A3: 504 sq ft (46.8 m2)  • Flues A1: 835 sq ft (77.6 m2) A3: 2,159 sq ft (200.6 m2)  • Firebox 215 sq ft (20.0 m2) Superheater: ​  • Heating area A1: 525 sq ft (48.8 m2) A3: 1,104 sq ft (102.6 m2) Cylinders Three Cylinder size 18.5 in × 26 in (470 mm × 660 mm) (A3) 19 in × 26 in (483 mm × 660 mm) (A3) 20 in × 26 in (508 mm × 660 mm) (A1/A3) Valve gear Outside:Walschaerts Inside: Gresley conjugated Valve type Piston valves

Performance figures Maximum speed 108 mph (174 km/h) Tractive effort A1: 29,835 lbf (132.71 kN) A3: 30,362 lbf (135.06 kN) (18.5x26 cylinders) 32,910 lbf (146.39 kN) (19x26 cylinders) 36,465 lbf (162.20 kN) (20x26 cylinders)

Career Operators London and North Eastern Railway British Railways Power class BR: 7P6F Axle load class Route Availability: 9 Withdrawn 1959–1966 Preserved One: 4472 Disposition One preserved, remainder scrapped

The London and North Eastern Railway LNER Gresley Classes A1 and A3 locomotives represented two distinct stages in the history of the British 4-6-2 "Pacific" steam locomotives designed by Nigel Gresley. They were designed for main line passenger services, initially on the Great Northern Railway (GNR), a constituent company of the London and North Eastern Railway after the amalgamation of 1923, for which they became a standard design. The change in class designation to A3 reflected the fitting to the same chassis of a higher pressure boiler with a greater superheating surface and a small reduction in cylinder diameter, leading to an increase in locomotive weight. Eventually all of the A1 locomotives were rebuilt, most to A3 specifications, but no. 4470 was completely rebuilt as Class A1/1.

The names for the locomotives came from a variety of sources. The first, Great Northern, was named after its parent company. Others were given the names of high-ranking railway officials, but most were given the names of famous racehorses. One was named after the company's most famous long-distance passenger train, the Flying Scotsman. Flying Scotsman is the sole survivor of the class to be preserved.

The new Pacific locomotives were built at the Doncaster "Plant" in 1922 to the design of Nigel Gresley, who had become Chief Mechanical Engineer of the GNR in 1911. The intention was to produce an engine able to handle, without assistance, mainline express services that were reaching the limits of the capacity of the Ivatt large-boilered Atlantics.

Gresley's initial Pacific project of 1915 was for an elongated version of the Ivatt Atlantic design with four cylinders. Finally realising that he was in a design impasse, he took as a model the new American Pennsylvania Railroad class K4 Pacific of 1914. This in turn had been updated from a series of prototypes scientifically developed in 1910 under Francis J. Cole, Alco's Chief Consulting Engineer at Schenectady and the Pennsylvania's K29 Alco prototype of 1911, also designed by Cole. Descriptions of those locomotives appeared in the British technical press at the time and gave Gresley the elements necessary to design a thoroughly up-to-date locomotive.