Upon becoming Chief Mechanical Engineer of the LNER, Thompson sought to create an unstreamlined, mixed traffic version of Gresley’s A4 Pacific locomotives. Being unable to secure permission to construct new locomotives, Thompson decided to rebuild the 2-8-2 P2 Class locomotives as the new A2/2 Class. Thompson advocated divided drive, a system in which the middle cylinder drove the forward two of the six driving wheels whilst the outside cylinders drove the middle two.

Due to his quest for standardisation, this arrangement necessitated the middle cylinder to be placed further forward than normal and the outside cylinders further back, behind the leading bogie, so that standard connecting rods could be used for all cylinders. Although the new designs retained much of the P2’s power despite their lighter weight, wheel slip issues made them unsuitable for the routes the P2’s had been designed for. P2 No. 2002 ‘Earl Marischal’ was rebuilt to become a A2/2 in June 1944, before being renumbered 502 in 1946 and 60502 upon the nationalisation of the railways. After becoming a A2/2, ‘Earl Marischal’ returned to Scotland before being moved south of the border to the York Shed at the end of 1949. The locomotive was withdrawn for service in 1961