Built: 1920 – 1937
Built for: GNR / LNER
Designed by: Sir Nigel Gresley
Duties: mixed traffic
• Two tender variants modelled
• Sprung buffers
The Class K3 ‘Mogul’ was primarily a development from earlier achievements by Nigel Gresley on the Great Northern Railway. His predecessor, Henry Ivatt, had already implemented the GNR’s letter ‘H’ classification system for the 20 engines described as Class H1 purchased from the Baldwin Company, USA. The letter ‘H’ indicated a 2-6-0 locomotive. Gresley’s pioneer class of 1912 was in essence an Ivatt 0-6-0 with pony truck and outside cylinders; this received the designation Class H2. A few years later, a development of this class with a larger boiler became Class H3. All were two-cylinder locomotives.
Subsequently, 1920 saw the introduction of a version with an even larger boiler and three cylinders described as Class H3. After the Grouping they became reclassified K1, K2 and K3 by the LNER in order of their introduction. Altogether, 183 Class K3 locomotives were constructed between 1924 and 1937 at a variety of workshops in compliance with LNER standards in addition to the ten GNR versions outshopped in 1920.
The emergence of Gresley’s Class V2 2-6-2 locomotives in 1936 saw the end of K3 construction. The 193 examples of K3 in traffic were used all over the former LNER system. The first K3 was withdrawn in February 1958 and by December 1962 all were gone. Not one example survived into preservation.