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Sir Nigel Gresley
Sustaining the legacy
Class K3
The Great Northern Railway Class H4 (LNER class K3) was a class of 2-6-0 steam locomotive designed by Nigel Gresley for mixed-traffic work.
The type was a more powerful development of the earlier class H3 (LNER class K2) class and was notable at the time, as the 6-foot-diameter 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.
The concept for the class K3 2-6-0 began in August 1917 when Gresley started to consider a new express goods engine for the Great Northern Railway (GNR) based on his class K2 2-6-0 (GNR class H3), but with a higher boiler pressure and larger cylinders. However, Gresley’s three-cylinder class O2 2-8-0 mineral locomotive, incorporating his patent ‘conjugated’ valve gear on the middle cylinder, was quickly deemed a success and Gresley announced that his future designs would concentrate on three-cylinder designs.
With three cylinders, he reduced the cylinder diameter to 18.5in but kept the boiler pressure at 180psi, with the net effect of an increase in tractive effort of 36 per cent over the class K2s. The boiler was enlarged to a then-unprecedented 6ft diameter, in order provide an adequate supply of steam. The outside cylinders were almost horizontal, but the inside cylinder was steeply inclined to clear the leading coupled axle.
Although very similar to the class K1s and class K2s, the class K3s looked different due to their large diameter boilers and stout boiler mountings. The cab continued the austere style started by Ivatt. Later batches of K3s would introduce side windows and padded seats to the design.
The first ten locomotives (Nos. 1000-9) were constructed at the GNR’s Doncaster Works between 1920 and 1921. Their advent coincided with the coal strike of 1921. Although intended for fast goods work, the strike meant they were often used on express passenger services as an economy measure. The class K3s managed this very well, and quickly made a name for themselves hauling trains up to twenty bogies in size.
The class K3 became a Group Standard design quickly after Grouping in 1923, and in total 193 locomotives would be built in seven batches between 1920 and 1937 at Doncaster and Darlington Works, Armstrong Whitworth, Robert Stephenson and Company and the North British Locomotive Company. Construction only stopped after the new class V2s had proven themselves as good replacements.
Each batch would show minor refinements, so between 1923 and 1935 each batch was classified chronologically by its part number. Due to the differences being deemed minor in nature, classes K3/4, K3/5, and K3/6 were merged in with class K3/2 in 1935. The original ten K3/1s were built to the larger GNR loading gauge, but were reclassified as class K3/2 when they were cut down to the Composite LNER loading gauge. The last K3/1 was cut down and reclassified in 1940. Usage of the K3/2 and K3/3 class parts was discontinued with Nationalisation in 1948.
One of the biggest changes was the introduction of long lap valves in 1928. These valves had already resulted in improvements in coal economy on the class A1 Pacifics. No. 134 was fitted in October 1928 as a trial and quickly showed a considerable improvement in coal consumption. All future K3s would be built with long lap valves, and the existing class K3s were converted by 1936.
The class K3s were used throughout the LNER network. The first batch of ten were allocated to King’s Cross, Peterborough (New England) and Doncaster; and would remain there until the 1930s when transfers to the GC (Great Central) and GE (Great Eastern) areas occurred. At Grouping, the GN section was well equipped with mixed-traffic 2-6-0s (classes K1, K2 and K3). Of the next sixty class K3s to be built, thirty four were allocated to the GN Section, displacing class K1s and class K2s to other areas of the LNER network. The general effect was to allow slightly larger braked goods trains to run at slightly faster speeds. The class K3s operated the express goods trains, whilst the class K2s operated the slower services. They were excellent mixed-traffic locomotives, although their large size restricted their route availability. In their later years, they were primarily employed on vacuum-fitted freight traffic.
In 1945, Edward Thompson rebuilt class K3 No. 206 into a two-cylinder engine forming the LNER class K5. No more were so treated, although some later received class K5 type boilers. All of these boilers were operated at the class K3 pressure of 180psi.
The original ten locomotives were numbered No. 1000–1009 by the GNR, and became LNER No. 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 class K3s and class K5 were renumbered No. 1800–1992, and they later became British Railways No. 61800–61992.
All were withdrawn and scrapped between 1959 and 1962; the class K5 went in 1960. Three were kept as stationary boilers, with the last two being finally withdrawn in 1965. None have survived into preservation.
