LNER K3 2-6-0

The LNER K3 Class was a fleet of 193 three-cylinder 2-6-0 mixed-traffic steam locomotives designed by Sir Nigel Gresley for the Great Northern Railway in 1920 and continued in production by the LNER through to 1937. The K3 was distinguished by its very large 6 ft diameter boiler, the biggest fitted to any British 2-6-0, and was used principally for fast fitted freight and heavy summer Saturday passenger relief work. None of the 193 engines survived into preservation, although the class was one of the most numerous of Gresley's LNER mogul designs.

Gresley designed the K3 as a more powerful development of his earlier GNR K2 mogul of 1912. The 6 ft diameter boiler was the largest ever fitted to a British 2-6-0 and gave the class exceptional power at the cost of a high centre of gravity that produced rough riding at speed; the class's nickname "Jazzers" came from this characteristic. 193 were built over 17 years at Doncaster, Darlington, Armstrong Whitworth, and the North British Locomotive Company.

The class was widely allocated across the LNER and worked fitted freight, summer Saturday passenger reliefs, and heavy local passenger services. Major depots included Doncaster, Sheffield Darnall, Cambridge, Norwich Thorpe, Heaton, York, Edinburgh St Margarets, and Aberdeen Ferryhill. Withdrawals began in the late 1950s as Type 4 diesels arrived in numbers, and the class was extinct by 1962.

Despite the class's technical interest and the Gresley association, none of the 193 K3s have survived into preservation. The class was scrapped at Doncaster, Darlington, and at Cohen's yards during the late 1950s and early 1960s. There has been periodic enthusiast interest in a new-build K3 but no project has been formally announced.