Until the mid-1920s, the LMS had followed the Midland Railway's small engine policy, which meant that it had no locomotives of sufficient power for its expresses on the West Coast Main Line.

However, in 1926 the Chief Mechanical Engineer, Henry Fowler, began the design of a compound Pacific express locomotive.

[1] Following the success of the Castle 4-6-0 in working on the LMS, a decision was taken to cancel Fowler's Pacific project, and to replace it with a 4-6-0 with three cylinders and a simple-expansion steam circuit.

The North British, with its extensive drawing office and two works, possessed sufficient capacity to expedite the order within a year.

Fowler took little part in the design process, which was carried out by Herbert Chambers, Chief Draughtsman at Derby, and his staff.

[citation needed] They were initially named after regiments of the British Army, and after historical LNWR locomotives.

[citation needed] In 1933, the LMS was invited to send a locomotive and train to the Century of Progress International Exposition in Chicago, USA.

[5][6] The rebuilt locomotive assumed the identity of 6100 Royal Scot with (on its return from the USA) an enlarged nameplate with details of its appearance at the exhibition.

[7][4] LMS 6399 Fury, built in 1929, was an unsuccessful experimental prototype locomotive with a high-pressure, water tube boiler and compound 3-cylinder drive, based on the Royal Scot.

The new 'Rebuilt Scot' design was carried out under the auspices of William Stanier, who was then engaged on war work, so was actually undertaken by George Ivatt and E.S.

Models to 00 scale of the Royal Scot in both unrebuilt and rebuilt forms have been produced by several manufacturers, and each has been available in several liveries with a variety of numbers and names.

[12] Bachmann took over the tooling for both of the Mainline locomotives, and did do several production runs,[15] with the ultimate intention of re-tooling the design to upgrade it to modern standards and detailing, but unfortunately for them, Hornby beat them to it.

Graham Farish released a British N gauge model in 2009, in LMS Black, and BR Brunswick Green liveries.

The erstwhile Kitmaster company produced an unpowered polystyrene injection moulded model kit for TT gauge.