LNER Thompson A2/1 Class

The LNER Thompson A2/1 Class was a series of four 4-6-2 Pacific express passenger locomotives rebuilt by Edward Thompson in 1944 from Gresley's three-cylinder V2 2-6-2 Class engines, converting the V2s into Pacifics as part of Thompson's programme of standardisation and of departing from Gresley's conjugated valve gear. The A2/1 rebuilding converted the V2's 2-6-2 wheel arrangement into a 4-6-2 Pacific by adding a leading pony truck, while also replacing the three-cylinder conjugated valve gear with Thompson's preferred separate Walschaerts valve gear and adopting his standard divided drive arrangement.

Thompson's rationale for the A2/1 rebuilding was partly practical — the V2s were suffering from maintenance difficulties with the conjugated valve gear — and partly philosophical: Thompson believed that Gresley's conjugated gear was fundamentally unreliable and sought to eliminate it wherever possible across the LNER fleet. The four A2/1 rebuilds were not universally regarded as an improvement over the original V2 in service terms, and the conversion cost was substantial relative to the operational benefit.

The A2/1 Class gave service on LNER and BR express duties under their new Pacific configuration. None was preserved. The V2 Class from which they were rebuilt is well represented in preservation by Green Arrow at the National Railway Museum.