The LNER Class A1/1 consisted of a single 4-6-2 "Pacific" express passenger locomotive rebuilt in 1945 from an A1 class locomotive, by Edward Thompson. It was intended as the prototype of a new design of pacific locomotives improving the A4 design of Thompson's predecessor Sir Nigel Gresley. No further examples were built due to Thompson's retirement in 1946. Background When Edward Thompson was appointed Chief Mechanical Engineer of the London and North Eastern Railway in April 1941, he envisaged a new standardisation programme involving ten locomotive designs including two Pacific types. These were an express passenger type (designated A1) with driving wheels and a ‘heavy passenger and freight’ type (designated A2) with driving wheels. He was not able to proceed with his plan due to the Second World War but did try out some of his ideas by rebuilding Nigel Gresley’s P2 class 2-8-2 as A2/2 pacifics and building the last four V2 class already on order as A2/1 pacifics. At last in July 1944 Thompson began work on designing his new A1 class incorporating everything learned from the twenty-plus years of Gresley's development of the Pacific locomotives along with the construction and operation of the rebuilt P2 and A2/1. Thompson had no desire to rebuild the Gresley A10 and A3 classes to the new specification as he believed they were an essential part of the LNER locomotive fleet, with Simon A.C. Martin suggesting that O.S. Nock's pamphlet produced for the LNER may have suggested so. Some commentators believed that he intended to rebuild one of the surviving Gresley pacifics of the A1 class to try out the new design. Design Thompson's A1/1 design differed from his previous designs by adopting a divided drive with the centre cylinder, where the inside connecting rod was of a different length to the outside one, ignoring the presumed advantages provided by an equal length connecting rods and the subsequent valve events. This gave an elongated look with the resulting wheelbase being long, even longer than the Gresley P2s. The final design omitted the inside Gresley conjugated valve gear in favour of three independent sets of Walschaerts valve gear. Steam was generated using a diagram No. 107 boiler, which was used on Gresley A4 locomotives, necessitating the use of A4 frames. The smokebox was carefully developed based on the practice set by the rebuilt P2 locomotives. Thompson followed Gresley's development with a double Kylchap