The A1 4-6-2 Pacifics were built between 1948 and 1949 at Doncaster and Darlington Works to a design of the LNER's Chief Mechanical Engineer, Arthur Peppercorn, following on from a project begun by his predecessor Thompson,who ordered the rebuilding of a veteran Gresley A1 which became No. 60113 GREAT NORTHERN. Forty-nine were built for hauling express passenger services on the East Coast Main Line but they were not completed until the LNER had ceased to exist, replace by British Railways. None of the original 49 Peppercorn A1s survived into preservation, with the last being scrapped in 1966, but a 50th Peppercorn A1, new build No. 60163 TORNADO, was completed in 2008. The locomotives were designed to cope with the heaviest passenger trains in the post-war period on the East Coast Main Line (London – York – Newcastle – Edinburgh – Aberdeen) which consisted normally of trains with up to 15 coaches and up to 550 tons. The Peppercorn A1s were able to pull such a train on the flat at a speed of 60–70 mph. The class used a double Kylchap chimney system and, like previous LNER Pacifics, had a 3-cylinder arrangement.