LB&SCR I2 & I4 classes
Side-view builder's photo of LB&SCR I2 class 4-4-2T.
Type and origin Power type Steam Designer D.E. Marsh Builder Brighton Works Build date 1907-1909 Total produced I2: 10; I4: 5
Specifications Configuration: ​  • Whyte 4-4-2T Gauge 4 ft 8+1⁄2 in (1,435 mm) standard gauge Leading dia. 3 ft 6 in (1.067 m) Driver dia. 5 ft 6 in (1.676 m) Trailing dia. 4 ft 0 in (1.219 m) Loco weight 68.5 long tons (69.6 t; 76.7 short tons) I2, 70.25 long tons (71.38 t; 78.68 short tons) I4 Fuel type Coal Water cap. 2,238 imp gal (10,170 L; 2,688 US gal) Boiler pressure 170 psi (12 bar; 1.2 MPa) Cylinders Two, inside Cylinder size 17.5 in × 26 in (444 mm × 660 mm)
Performance figures Tractive effort I2: 17,425 lbf (77.51 kN), I4: 17,790 lbf (79.13 kN)
Career Retired 1933-1940 Disposition All scrapped

The LBSCR I2 class was a class of 4-4-2 steam tank locomotives designed by D. E. Marsh for suburban passenger service on the London, Brighton and South Coast Railway. The I4 class were of the same design but incorporated a superheated boiler.

In 1907, following the failure of his I1 class, Douglas Earle Marsh sought to fix some of their flaws with a new 4-4-2T design with a longer wheelbase, larger boiler and detailed changes to the front end.^[1] In the original order, five of the locomotives would incorporate a superheated boiler to be supplied by the North British Locomotive Company, and the remainder traditional saturated steam boilers from Brighton railway works.^[1] In the event, the superheated boilers were delayed in construction and so all ten I2 locomotives had traditional boilers.^[1]

When the superheated boilers eventually arrived they were used for five further locomotives of the same design as the I2, but these were classified as I4.^[1]

However neither the I2 nor I4 class addressed the fundamental problems with the I1 class, that being a small firebox.^[2] As a result, the two classes had relatively short lives working lightly loaded secondary services, and the Stroudley D1 and Billinton E4 classes which they were meant to replace continued working.

LB&SCR numbers were 11-20 and 31-35. The Southern Railway, which acquired the locomotives in 1923, initially numbered them B11-B20, B31-35 and later 2011-2020, 2031-2035.

All the I2 were withdrawn between 1933 and 1939^[3] but two locomotives, numbers 2013 and 2019, saw further service on the Longmoor Military Railway where they survived until at least 1947. There they were numbered 2400 and 2401 respectively. These numbers were later changed to 72400 and 72401.^[4] The I4 class were withdrawn between 1936 and 1940. No examples of either class have been preserved.

• Bradley, D.L. (1974). Locomotives of the London Brighton and South Coast Railway: Part 3. Railway Correspondence and Travel Society.
• Dendy Marshall, C. F. (1988). History of the Southern Railway. Ian Allan. p. 271. ISBN 0-7110-0059-X.

• Marsh I2 Class 4-4-2T at semgonline.com