LNER Thompson A1/1

LNER No. 113 / A1/1 was a unique rebuilt Pacific locomotive created by Edward Thompson in 1945 from Gresley's original A1 Pacific prototype — No. 4470 Great Northern — which had been the first Gresley Pacific, built in 1922 and the progenitor of the entire A1/A3 family that produced Flying Scotsman and Mallard. Thompson's decision to rebuild the original Great Northern was one of his most controversial acts as CME, as it destroyed the historical integrity of the first LNER Pacific while producing a rebuilt locomotive that was not regarded as a significant improvement over the original.

Thompson rebuilt No. 4470 in 1945 to his own A1 specification: divided drive, longer wheelbase, separate Walschaerts valve gear for each cylinder (replacing Gresley's conjugated gear), and Thompson's standard cab and tender design. The rebuilt locomotive was renumbered 113 and reclassified A1/1 to distinguish it from both the original A1s and Peppercorn's subsequent new-build A1 Pacific class. The A1/1 designation indicated a one-off: a single locomotive in a class of its own.

The rebuilt Great Northern (now No. 113) gave service under BR but was not regarded as exceptional, and the destruction of the original prototype locomotive for a controversial rebuild that produced no clear improvement was widely criticised. No. 113 was withdrawn in 1945 and scrapped. The original Great Northern in its 1922 Gresley form was not preserved, a loss as significant as any in the national collection.