SR N1 class

SECR/SR N1 class
The N1 class prototype, No. 822 seen here at the SECR's Ashford works in 1922. Smoke deflectors were added during the early 1930s. Note the linkage for Holcroft's inside valve gear, connecting the right-hand combination lever assembly and the inside cylinder
Type and origin Power type Steam Designer Richard Maunsell Builder SECR/SR Ashford Works Build date 1922 (1), 1934 (5) Total produced 6
Specifications Configuration: ​  • Whyte 2-6-0 ('mogul')  • UIC 1′C h3 Gauge 4 ft 8 1⁄2 in (1,435 mm) standard gauge Leading dia. 3 ft 1 in (0.940 m) Driver dia. 5 ft 6 in (1.676 m) Length 57 ft 10 in (17.63 m) Total weight 106 long tons 13 cwt (238,900 lb or 108.4 t) (119.5 short tons) Fuel type Coal Fuel capacity 5 long tons (5.1 t; 5.6 short tons) Water cap A822: 3,500 imperial gallons (15,900 l; 4,200 US gal) A876–A880: 4,000 imperial gallons (18,200 l; 4,800 US gal) Boiler pressure 200 lbf/in2 (13.79 bar; 1.38 MPa) Cylinders Three Cylinder size 16 in × 26 in (406 mm × 660 mm)
Performance figures Tractive effort 27,695 lbf (123.19 kN)
Career Operators South Eastern and Chatham Railway → Southern Railway → British Railways (Southern Region) Class SECR / SR: N1 Power class BR: 4P5FB Withdrawn 1962 Disposition All scrapped

The SECR N1 class was a type of 3-cylinder 2-6-0 ('mogul') steam locomotive designed by Richard Maunsell for mixed traffic duties, initially on the South Eastern and Chatham Railway (SECR), and later operated for the Southern Railway (SR). The N1 was a development of the basic principles established by the Great Western Railway's (GWR) Chief Mechanical Engineer (CME) George Jackson Churchward and by Maunsell's previous N class design.

The N1 prototype was the result of modifications made to N class No. 822 during construction in 1922. The locomotive became operational in 1923 and used parts interchangeable with other Maunsell locomotive classes. The prototype N1 was the only member of the class constructed before the SECR became part of the Southern Railway at the Grouping in 1923, and featured a variant of the Gresley conjugated valve gear designed by Harold Holcroft. The class set the precedent for the Southern Railway's subsequent 3-cylinder designs.

The N1s compared favourably with the N class, although the type showed little improvement in performance. More of the class were built when it became clear that the type's smaller cylinders provided greater route availability. A total of six engines were built. The N1 class was primarily used on the Eastern section of the Southern Railway network, and used by the Southern Region of British Railways (BR) from 1948. The N1s gave valuable service until they were withdrawn in 1962. None were preserved.