SECR K and SR K1 classes

SECR K & SR K1 (River) classes[1]
The prototype K class No. 790 (later named River Avon) under SECR ownership. The class was named after rivers flowing within the Southern Railway's operating area.
Type and origin Power type Steam Designer Richard Maunsell Builder K: Ashford Works (1)  Brighton Works (10)  Armstrong Whitworth (9) K1: Ashford Works (1) Build date 1917, 1925–1926 Total produced K: 20 K1: 1
Specifications Configuration: ​  • Whyte 2-6-4T  • UIC K: 1′C2′ h2t K1: 1′C2′ h3t Gauge 4 ft 8+1⁄2 in (1,435 mm) standard gauge Leading dia. 3 ft 1 in (0.940 m) Driver dia. 6 ft 0 in (1.829 m) Trailing dia. 3 ft 1 in (0.940 m) Wheelbase 35 ft 10 in (10.922 m) Length 43 ft 6+1⁄4 in (13.265 m) Height 12 ft 11+3⁄8 in (3.947 m) Axle load K: 18.50 long tons (18.80 t; 20.72 short tons) Adhesive weight K: 52.75 long tons (53.60 t; 59.08 short tons) Loco weight K: 82.75 long tons (84.08 t; 92.68 short tons) (790 only) K: 84 long tons (85 t; 94 short tons) (A791-A809) K1: 88.75 long tons (90.17 t; 99.40 short tons) Fuel type Coal Fuel capacity 2.50 long tons (2.54 t; 2.80 short tons) Water cap. 2,000 imp gal (9,100 L; 2,400 US gal) Boiler pressure 200 lbf/in2 (13.79 bar; 1.38 MPa) Cylinders K: Two, outside K1: Three Cylinder size K: 19 in × 28 in (483 mm × 711 mm) K1: 16 in × 28 in (406 mm × 711 mm) Valve gear K: Walschaerts K1 (outside): Walschaerts  (inside): Holcroft
Performance figures Tractive effort K: 23,866 lbf (106.161 kN) K1: 25,387 lbf (112.927 kN)
Career Operators South Eastern and Chatham Railway → Southern Railway Class K and K1 classes Numbers K: 790–809 K1: 890 Official name River class Nicknames Rolling Rivers Withdrawn 1927 Disposition All rebuilt to U or U1 class — One rebuild surviving

The SECR K class was a type of 2-6-4 tank locomotive designed in 1914 by Richard Maunsell for express passenger duties on the South Eastern and Chatham Railway (SECR), which operated between London and south-east England. The Southern Railway (SR) K1 class was a three-cylinder variant of the K class, designed in 1925 to suit a narrower loading gauge. They were among the first non-Great Western Railway (GWR) types to use and improve upon the basic design principles of power and standardisation established by GWR Chief Mechanical Engineer (CME) George Jackson Churchward.^[2] The locomotives were based on the GWR 4300 class, improved by the Midland Railway's ideals of simplicity and ease of maintenance.^[3]

The K class was designed to be mechanically similar to the SECR N class 2-6-0 mixed-traffic locomotives. The class was one of the earliest to use the 2-6-4 wheel arrangement in Britain.^[2] Production began towards the end of the First World War, and the prototype rolled out of Ashford Works three years after design work was completed due to wartime production constraints. The class replaced obsolete 4-4-0 passenger locomotives in an SECR fleet standardisation programme.

Twenty-one locomotives were built: twenty K class (two cylinders) and one K1 class (three cylinders), the first in 1917 and the remainder between 1925 and 1926. They operated over the Eastern section of the Southern Railway network and were given the names of rivers, being referred as the River class from 1925. Crews referred to the K and K1 classes as "Rolling Rivers" because of their instability when travelling at speed. They were rebuilt as 2-cylinder SR U class and 3-cylinder SR U1 class 2-6-0s (respectively) following a railway accident at Sevenoaks, Kent in 1927. They continued in service with British Railways (BR) until the last was withdrawn in 1966. One K class rebuild (No. 31806) is preserved on the Swanage Railway in Dorset and still operational today.