The 3521 Class were forty tank locomotives designed by William Dean to haul passenger trains on the Great Western Railway. They were introduced as locomotives in 1887, but were quickly altered to become s to improve their running. Following two serious accidents they were further altered from 1899 to run as tender locomotives, in which form the last was withdrawn in 1934.
Locomotives 0-4-2T standard gauge The first twenty locomotives were turned out in 1887 as locomotives for services on the lines.
3521 3522 3523 3524 3525 3526 3527 3528 3529 3530 3531 3532 3533 3534 3535 3536 3537 3538 3539 3540
0-4-2ST broad gauge In 1888 a further batch of twenty were ordered as s for the broad gauge lines in Devon and Cornwall.
3541 (1888 - 1890) 3542 (1888 - 1891) 3543 (1888 - 1891) 3544 (1888 - 1890) 3545 (1888 - 1891) 3546 (1888 - 1890) 3547 (1888 - 1891) 3548 (1888 - 1891) 3549 (1888 - 1891) 3550 (1888 - 1890) 3551 (1888 - 1890) 3552 (1888 - 1890) 3553 (1888 - 1890) 3554 (1889 - 1891) 3555 (1889 - 1890) 3556 (1889 - 1890) 3557 (1889 - 1891) 3558 (1889 - 1890) 3559 (1889 - 1890)
0-4-4T broad gauge
Due to the unsteady running of the s, the last of the order, 3560, was turned out in August 1889 as a bogie side tank. The remainder of the class were altered to a similar layout over the following two years. 3560 was slightly different at this time, having a bogie that was shorter and an overall wheelbase of , rather than the of the converted locomotives.
3541 (1890 - 1892) 3542 (1891 - 1892) 3544 (1890 - 1892) 3545 (1891 - 1892) 3546 (1890 - 1892) 3548 (1891 - 1892) 3549 (1891 - 1892) 3550 (1890 - 1892) 3551 (1890 - 1892) 3552 (1890 - 1892) 3553 (1890 - 1892) 3554 (1891 - 1892) 3555 (1890 - 1892) 3556 (1890 - 1892) 3557 (1891 - 1892) 3558 (1890 - 1892) 3559 (1890 - 1892) 3560 (1889 - 1892)
0-4-4T standard gauge
The standard gauge s were converted to s 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.
3521 3522 3523 3524 3525 3526 3527 3528 3529 3530 3531 3532 3533 3534 3535 3536 3537 3538 3539 3540 3541 (1892 - ) 3542 (1892 - ) 3543 (1891 - ) 3544 (1892 - ) 3545 (1892 - ) 3546 (1892 - ) 3547 (1891 - ) 3548 (1892 - ) 3549 (1892 - ) 3550 (1892 - ) 3551 (1892 - ) 3552 (1892 - ) 3553 (1892 - ) 3554 (1892 - ) 3555 (1892 - ) 3556 (1892 - ) 3557 (1892 - ) 3558 (1892 - ) 3559 (1892 - ) 3560 (1892 - 1899)
4-4-0 standard gauge All forty locomotives were rebuilt as 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 states that twenty-six received Standard No 3 boilers.)
Holcroft was of the opinion that the original inside and outside frames were modified whereas Le Fleming was of the opinion that new inside frames would have been required. However, as the modification also increased the coupled wheelbase from to , it is unlikely that much of the original framing was re-used.
Two locomotives, 3521 and 3546, were sold to the Cambrian Railways in August 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 amalgamated at the start of 1922.
Accidents and incidents On 13 April 1895, locomotives 3536 and 3537, hauling the Cornishman, exceeded the speed limit by , damaging the track. A passenger train hauled by 3521 and 3548 consequently derailed between and Bodmin Road, Cornwall. In 1898, locomotive 3542 derailed near Penryn, Cornwall whilst hauling a mail train. The locomotive rolled down an embankment, killing the driver. The accident was caused by a combination of the condition of the track and the locomotive oscillating. Following this the whole class was rebuilt as tender locomotives.
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