LNER Gresley Classes A1 and A3

LNER Gresley Classes A1 and A3[1]
Class A1 4474 Victor Wild at Kings Cross Station Yard
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 (78) Rebuild date 1928–1949 Number rebuilt 51
Specifications Configuration: ​  • Whyte 4-6-2  • UIC 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) Height 13 ft 1 in (3.99 m) (First 11 A1s were cut back from 13 ft 4 in (4.06 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: ​  • Grate area 41.25 sq ft (3.832 m2) Boiler pressure A1: 180 psi (1.24 MPa) A3: 220 psi (1.52 MPa) Heating surface: ​  • Firebox 215 sq ft (20.0 m2)  • 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) Superheater: ​  • Heating area A1: 525 sq ft (48.8 m2) A3: 1,104 sq ft (102.6 m2) Cylinders Three Cylinder size 18.25 in × 26 in (464 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 Loco brake Vacuum Train brakes Vacuum
Performance figures Tractive effort A1: 29,835 lbf (132.71 kN) A3: 30,362 lbf (135.06 kN) (18.5×26 cylinders) 32,910 lbf (146.39 kN) (19×26 cylinders) 36,465 lbf (162.20 kN) (20×26 cylinders)
Career Operators London and North Eastern Railway British Railways Power class BR: 7P6F Numbers LNER (until 1945/46): 2543–2582, 2595–2599, 2743–2752, 2795–2797, 4470–4481, 2500–2508; LNER (from 1945/46); 35–112; BR: 60035–60112 Axle load class Route Availability: 9 Locale East Coast Main Line Withdrawn 1959–1966 Preserved One: 4472 Disposition One rebuilt as Thompson A1/1; one preserved, one boiler preserved; remainder scrapped

The London and North Eastern Railway 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 and later express 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 member of the class to be preserved.