GWR 3521 Class

The first twenty locomotives were turned out in 1887 as 0-4-2T locomotives for services on the 4 ft 8 ¹⁄₂ in (1,435 mm) standard gauge lines.

In 1888 a further batch of twenty were ordered as 0-4-2ST saddle tanks for the 7 ft ¹⁄₄ in (2,140 mm)broad gauge lines in Devon and Cornwall.

Due to the unsteady running of the 0-4-2STs, the last of the order, 3660, was turned out in August 1889 as a 0-4-4T bogie side tank. The remainder of the class were altered to a similar layout over the following two years. 3660 was slightly different at this time, having a bogie that was six inches (152 mm) shorter and an overall wheelbase of 20 ft 4 in (6.20 m), rather than the 21 ft 4 in (6.50 m) of the converted locomotives.

The standard gauge 0-4-2Ts were converted to 0-4-4Ts in the same manner as the broad gauge locomotives, which were all eventually converted to standard gauge. By the end of 1892 the whole class of forty locomotives was to one standard design for the first time.

All forty 0-4-4T locomotives were rebuilt as 4-4-0 tender locomotives between 1899 and 1902. Twenty six locos retained their parallel domed boilers while fourteen received new Standard No 3 parallel domeless boilers (later replaced by the taper barrel version of that type).

Holcroft[1] was of the opinion that the original inside and outside frames were modified whereas Le Fleming[2] was of the opinion that new inside frames would have been required. However, as the modification also increased the coupled wheelbase from 7 ft 4 in to 8 ft 6 in it is unlikely that much of the original framing was re-used.

Two locomotives, 3521 and 3546, were transferred to the Cambrian Railways in 1921 to replace locomotives destroyed in the Abermule accident. They were allocated Cambrian numbers 82 and 95 respectively but these were never carried, the two locomotives being returned to the Great Western Railway with their original numbers when the two railways were grouped together in 1922.