420 Class
The NBR 420 Class was a development of Thomas Wheatley's pioneering 224 Class, extending the North British Railway's use of the inside-cylinder 4-4-0 wheel arrangement that Wheatley had introduced to Britain in 1871. Built at Cowlairs Works in 1873, they were a larger and more capable version of the formula, consolidating the 4-4-0 as the NBR's standard express type at a time when the configuration was still a novelty on most British railways.
Wheatley retained the essential layout of the 224 Class — inside cylinders, four-wheel leading bogie, and large coupled driving wheels — but specified a more substantial boiler and greater cylinder dimensions to give the 420s a meaningful improvement in tractive effort. The class worked NBR express services between Edinburgh, Glasgow, and the Anglo-Scottish border connections, routes that required reliable and capable motive power. The 6 ft 6 in coupled wheels gave a good turn of speed on the relatively favourable gradients of the main NBR routes.
Wheatley was replaced as Locomotive Superintendent by Dugald Drummond in 1875, a change that brought a marked shift in locomotive policy at Cowlairs. Drummond introduced his own designs, and the Wheatley 4-4-0s — both the 224 and 420 classes — were progressively displaced from express work. None of the 420 Class was preserved.
Design and development
The 420 Class followed directly from Wheatley's 224 Class of 1871, retaining the inside-cylinder 4-4-0 layout but with a more substantial boiler and larger cylinders. Built at Cowlairs Works in 1873, they were the NBR's standard express type until Drummond's arrival in 1875 brought new locomotive policy to the railway.
Service and withdrawals
The 420 Class worked NBR express services from 1873. With Drummond's appointment as Locomotive Superintendent in 1875, the Wheatley designs were gradually superseded by Drummond's own 4-4-0s. All were withdrawn and scrapped; none was preserved.
Identification features
Inside-cylinder 4-4-0 with 6 ft 6 in coupled wheels and leading 4-wheel bogie.
Notable locomotives
- Various — none preserved
Allocations and regions
Worked NBR express services between Edinburgh, Glasgow, and the English border connections from 1873.
