Forty-nine were built for hauling express passenger services on the East Coast Main Line owned by LNER's successor, British Railways' North Eastern Region.

Thompson rebuilt the pioneer LNER Pacific Great Northern in 1945; originally this was the new Class A1, but the rebuild was not repeated.

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 class used a double Kylchap chimney system and, like previous LNER Pacifics, had a 3-cylinder arrangement.

However, in 2008, a brand new 50th A1 based on the original Peppercorn patterns, 60163 Tornado, was completed as the evolved member of the class.