LNER Class S1

Great Central Railway class 8H
69901 at Dunford Bridge on the Woodhead Line in 1950
Type and origin Power type Steam Designer John G. Robinson Build date 1908 (4), 1932 (2) Total produced 6
Specifications Configuration: ​  • Whyte 0-8-4T  • UIC D2′ n3t, later D2′ h3t Gauge 4 ft 8 1⁄2 in (1,435 mm) Driver dia. 4 ft 8 in (1.422 m) Trailing dia. 3 ft 2 in (0.965 m) Fuel type Coal Boiler pressure 180 psi (1.24 MPa) Cylinders Three Cylinder size 18 in × 26 in (457 mm × 660 mm) Valve gear Stephenson Valve type Slide valves
Performance figures Tractive effort 34,525 lbf (153.6 kN)
Career Operators Great Central Railway → London and North Eastern Railway → British Railways Class GCR: 8H LNER: S1 Numbers GCR: 1170–1173 LNER: 6170–6173; later 9900–9905 BR: 69900–69905 Withdrawn 1955–1957 Disposition All scrapped

The Great Central Railway Class 8H (LNER Class S1) was a class of 0-8-4T steam tank locomotives designed by John G. Robinson for hump shunting at Wath marshalling yard.

Four locomotives were built in 1907/1908 for the Great Central Railway. They were fitted with three cylinders. This gave a more even torque than with a 2-cylinder locomotive and reduced the risk of wheelslip under heavy load. All four passed into London and North Eastern Railway ownership at the 1923 grouping. At the time all four locomotives were allocated to Mexborough engine shed.

These were powerful locomotives but even more power was required so, in 1930, one locomotive was fitted with a superheater and a booster engine and classified S1/2. Two new locomotives (with superheaters and boosters) were built by the LNER in 1932 and classified S1/3. The remaining (non-booster) locomotives were classified S1/1 and were also fitted with superheaters. All the boosters were removed in 1943.

All six locomotives passed into British Railways ownership in 1948 and were numbered 69900-69905.

For terminology, see Steam locomotive components