LNER Thompson A2/2 Class

The LNER Thompson A2/2 Class was a series of six 4-6-2 Pacific express passenger locomotives rebuilt by Edward Thompson in 1944 from Gresley's P2 Class 2-8-2 Mikado locomotives, converting the massive eight-coupled P2s — designed specifically for the demanding Edinburgh–Aberdeen route with its sharp curves and severe gradients — into more orthodox Pacific configuration. The P2 rebuilding was one of Thompson's most significant and controversial decisions: the P2 Class, with its distinctive streamlined appearance and wheel arrangement unique in British express locomotive practice, was effectively destroyed as a class by the conversion.

Gresley's P2 Class had been designed in 1934 for the Edinburgh–Aberdeen route, where the severe curves and gradients south of Dundee demanded a locomotive with more adhesion than a Pacific could provide but with the steaming power for sustained express running. The 2-8-2 Mikado with eight coupled wheels was Gresley's solution, and the six P2s — Cock o' the North, Earl Marischal, Lord President, Mons Meg, Thane of Fife, and Wolf of Badenoch — were among the most powerful and characterful express locomotives in Britain.

Thompson's conversion of the six P2s to A2/2 Pacifics destroyed their unique 2-8-2 configuration. The rebuilt locomotives, while technically competent, gave no better performance on the Aberdeen route than the Pacifics already available. The loss of the P2 Class — Britain's only 2-8-2 express Mikados — is widely regarded as one of the most regrettable acts in LNER locomotive history. A new-build P2 Prince of Wales is under construction by the P2 Steam Locomotive Company as of 2026, seeking to recreate what was lost.