LNWR Class B

The London and North Western Railway Class B was a class of steam locomotives introduced in 1901. A development of the three-cylinder compound Class A, they had a 4-cylinder compound arrangement. 170 were built between 1901 and 1904.

Rebuilds

;Class E
Between 1904 and 1908, Webb's successor George Whale added a leading pony truck to 26 engines, making them s and taking them into Class E.
;Class F
Between 1906 and 1908, Whale also rebuilt 10 with larger Experiment-type boiler to Class F, again adding a leading pony truck..
;Class G
Neither of the above conversions was particularly successful and, as a result, 32 were rebuilt to Class G with 2-cylinder simple expansion between 1910 and 1917.
;Class G1
Whale's Successor Charles Bowen Cooke rebuilt a further 91 direct from Class B to 2-cylinder simple superheated LNWR Class G1. The rebuilds from Class B to Class G1 continued under LMS ownership between 1923 and 1927.
;Summary
A total of 170 locomotives were built but No. 134 was destroyed in a boiler explosion at Buxton on 11 November 1921 leaving 169. The rebuilds totalled 159, leaving 10 unrebuilt.

LMS ownership

The London, Midland and Scottish Railway inherited 53 unrebuilt Class B locomotives in 1923 and numbered them 8900–8952. The LMS continued to rebuild them to Class G1 and the number of unrebuilt locomotives dwindled to 10.

Withdrawal

The remaining 10 Class B locomotives were withdrawn in 1927–1928. None were preserved.