The London and North Eastern Railway (LNER) Class B17, also known as "Sandringham" or "Footballer" class was a class of 4-6-0 steam locomotive designed by Nigel Gresley for hauling passenger services on the Great Eastern Main Line. In total 73 were built. Background By 1926, the former GER B12 class locomotives were no longer able to cope with the heaviest express passenger trains on the Great Eastern Main Line between London and Cambridge, Ipswich and Norwich. Yet Gresley was unable to use his larger classes due to severe weight restrictions on the line. The requirement for a lightweight yet powerful 4-6-0 proved to be difficult to achieve. Design After several unsuccessful attempts by Doncaster Works to satisfy Gresley's specification, the contract for the detailed design and building of the class was given to the North British Locomotive Company in 1927. They used several features from a batch of A1 Pacifics they had built in 1924. The cab, cylinders, and motion had all been copied directly or slightly modified. Most of the boiler design was taken from the LNER Class K3 2-6-0 and LNER Class O2 2-8-0 designs. Darlington Works provided drawings for the bogies, and Stratford Works designs for the GE-type , tender. However, the two designs presented by the NB Loco Co. had an axle loading of 18 tons and 19 tons, respectively. The 18 ton design, being lighter, was chosen. Since it had an axle loading of 18 tons, 1 ton higher than the initial requirement of 17 tons, this meant that the B17’s route availability was “certain GER main lines” instead of the full range which was intended, although the LNER did accept the restriction. Due to weight restrictions it proved to be impossible for all three cylinders to drive the middle coupled axle. Therefore, the design used divided drive with the middle cylinder driving the leading axle and was positioned forward above the front bogie. The LNER also ordered some modifications, including an increase in cylinder size from to , and a lengthening of the firebox by with longer frames, and lighter springs. The design continued to prove problematic and the LNER eventually cancelled a penalty clause in the original contract. The first locomotive, No. 2802 Walsingham was delivered 30 November 1928, thirteen weeks late. Construction Ten locomotives were built by the North British Locomotive Company (works nos. 23803-12) during November and December, which were allocated