| Powertype: | Steam |
| GNR Class H4 LNER Class K3 | |
| Designer: | Nigel Gresley |
| Builddate: | 1920–1937 |
| Totalproduction: | 193 |
| Whytetype: | 2-6-0 |
| Driverdiameter: | 5feet |
| Locoweight: | 72.6LT |
| Cylindercount: | Three |
| Cylindersize: | 18.5x |
| Boilerpressure: | 1802NaN2 |
| Tractiveeffort: | 300301NaN1 |
| Operator: | Great Northern Railway, London and North Eastern Railway, British Railways |
| Operatorclass: | GNR: H4 LNER: K3 |
| Powerclass: | BR: 5P6F |
| Nicknames: | Jazzers |
| Withdrawndate: | 1959–1962 |
| Disposition: | All scrapped |
The Great Northern Railway Class H4 (classified K3 by the LNER) was a class of 2-6-0 steam locomotive designed for mixed-traffic work.
The type was a more powerful development of the earlier H3 (LNER K2) class and was notable at the time, as the 6adj=midNaNadj=mid boilers were the largest fitted to any British locomotive to that date. After formation of the London and North Eastern Railway, the type became known as class K3 and was adopted as an LNER standard design. They got the nickname "Jazzers" after the rhythm of their exhaust beat and the unbalanced gyratory movement.[1]
The first ten locomotives were built at the GNR's Doncaster Works in 1920, to the design of Nigel Gresley. Six further batches were built at Doncaster and Darlington Works, Armstrong Whitworth, Robert Stephenson and Company and the North British Locomotive Company. The last few of 193 examples were delivered in 1937.
They performed very well as mixed-traffic locomotives, although their large size restricted their route availability. The railway writer O. S. Nock described a journey on the footplate of a Mogul hauling a heavy express goods train in 1942.[2] In their latter years they were primarily employed on vacuum-fitted freight traffic.
See main article: Welwyn Garden City rail crashes.
In 1945, Edward Thompson rebuilt K3 No. 206 into an experimental, two-cylinder LNER Class K5. No more were rebuilt, although some later received K5-type boilers.
The original ten locomotives were numbered 1000–1009 by the GNR, and became LNER 4000–4009. Those built for the LNER were numbered haphazardly, filling in gaps in the LNER's numbering scheme. In the LNER's 1946 renumbering programme, the K3s and K5 were renumbered 1800–1992, and they later became British Railways 61800–61992.
All were withdrawn and scrapped between 1959 and 1962 while the K5 was scrapped in 1960. Three were kept as stationary boilers until 1965.[5]
It was announced in September 2018 that a new K3 was planned once the LNER Class V4 No. 3403 and LNER Class V3 projects are completed. The engine's number has not yet been confirmed, but is expected to be a replica since 61993 was allocated to an LNER Class K4 locomotive.[6]
