The Peppercorn Class A1 was designed by the last London & North Eastern Railway (LNER) Chief Mechanical Engineer, Arthur Peppercorn, who develpoped the designs for new A1 locomotives from Edward Thompson, as an evolution in LNER Pacific locomotive design, initiated by Nigel Gresley in 1922 with his original A1 Class (later rebuilt as A3 Class locomotives). The A1’s pedigree was second to none. Peppercorn’s locomotives were designed for the heaviest passenger train workloads on the East Coast Main Line, (London–York–Newcastle–Edinburgh–Aberdeen). These workhorses quickly proved their worth in the austere post-war years in terms of ease of maintenance, reliability and cost-effective operation. Indeed, developments in some of the later locomotives (fitted with roller bearings) meant that they became the most economic engines in their class. 49 were built at Doncaster and Darlington for the newly nationalised British Railways, between 1948–9.