They represent the ultimate development of Midland Railway's six coupled tender engines.

Many trainspotters knew them as "Duck Sixes", a nickname derived from their wheel arrangement.

Midland Railway locomotives were notorious for their short axle-box bearings, which were prone to overheating.

[citation needed] The LMS constructed 530 of the locomotives between 1923 and 1928, numbered sequentially from where the Midland engines left off from 4027.

Production of this was continued by Dapol after it acquired Airfix models in 1985, and were subsequently sold to Hornby in the late 1990s.