The 850 Class originally consisted of 50 locomotives comprising 48 new and two rebuilds. The rebuilds, Nos. 93 and 94, were supplied in 1875 and 1877 as renewals of the original Gooch locomotives of 1860. Later, as locomotives were rebuilt, the 120 locomotives of the 1901 class were incorporated into the 850 class to make a total of 170 locomotives. It has been claimed that nos. 1216-1227 were part of the 1901 class but this seems unlikely because they were built before the 1901 class was introduced. ;850 class
GWR nos.
Lot
Date built
Class
No. built
Notes
850-861
T
1874
850
12
862-873
V
1874-5
850
12
987-998
X
1875-6
850
12
93-94
-
1875-7
850
2
Rebuilds
1216-1227
Y
1876-7
850
12
Total
850
50
;1901 class
GWR nos.
Lot
Date built
Class
No. built
Notes
1901-1912
J2
1881-2
1901
12
1913-1924
L2
1882
1901
12
1925-1936
O2
1883-4
1901
12
1937-1948
Q2
1886-7
1901
12
1949-1960
R2
1888
1901
12
1961-1972
T2
1889-90
1901
12
1973-1984
V2
1890-91
1901
12
1985-96
X2
1891
1901
12
1997-2008
Y2
1891-92
1901
12
2009-2020
Z2
1894-5
1901
12
Total
1901
120
Modifications
The original 36 locomotives had their domes on the firebox, while the domes of the rest were on the middle of the boiler. The two classes became more uniform on rebuilding. All had full-length saddle-tanks; the wheels were diameter, the wheelbase was, and cylinders. They had inside frames. Pannier tanks were fitted from 1910, as rebuilding with Belpaire boilers took place, and from 1924 larger coal bunkers were fitted to many of the class. Seventeen locomotives retained their saddle tanks to the end. These were Nos. 855, 864, 873, 990, 991, 1216, 1904, 1913, 1925, 1932, 1933, 1939, 1944, 1963, 1981, 1984, & 2007.
Use
The engines were widely spread over the GWR network. They were useful for shunting in dock areas, as at Plymouth, Bristol, Llanelly, and Birkenhead, which was their last stronghold; in 1881-2 four went new to the Cornwall Minerals Railway. In 1906 and 1913 four were sold into industrial service, followed by four more in 1939. Up to 1927 the class were used on empty stock work at Paddington.
One 850 class and 43 former 1901 class locomotives passed into British Railways ownership in 1948 and were given the power classication "2F". According to Ian Allan, BR called them 1901 class. Ten were painted in BR unlined black, and the last examples survived as late as 1958, the last Armstrong engines in service. Only three unconverted saddle tanks survived into nationalisation. Of these two were from the 850 class, Nos. 1925 and 2007, which were withdrawn in 1951 and 1949. The other was GWR 2021 Class No. 2048 which was rebuilt as a pannier tank locomotive shortly after nationalisation and scrapped in 1952. Locomotive 1925 featured in the 1949 movieThe Chiltern Hundreds when it is seen arriving with a train at Denham station. Ian Allan gives the following details for the 1901 class in 1948: