The class was designed by Oliver Bulleid for use on the intensive freight turns experienced during wartime on the Southern Railway network.

The highly unusual and controversial design represents the ultimate development of the British 0-6-0 freight engine, capable of hauling trains that were usually allocated to much larger locomotives on other railways.

Built to essentially Victorian era principles,[5] these had been designed as replacements for many of the older 0-6-0s inherited by the Southern Railway in 1923,[6] and entered service in January 1938.

[8] The Southern Railway became an essential strategic war-asset because of its proximity to continental Europe, and needed to equip itself with adequate freight-handling capability to transport the vast quantities of supplies and troops required for the conflict.

The answer to this problem came from the drawing board of the Southern Railway's innovative Chief Mechanical Engineer, Oliver Bulleid, in the shape of the Q1.

Using the minimum amount of raw materials, and with all superfluous features stripped away, he produced in 1942 the most powerful 0-6-0 steam locomotive ever to run on Britain's railways.

[10] The class was one of several built under the wartime austerity regime, which stressed pure functionality above any considerations of style or decoration.

The unusual shape was also dictated by the use of materials; the lagging was made of a glass fibre insulation material known as 'Idaglass', which, although cheap and plentiful during the war years, could not support any weight, and therefore a separate casing was required which followed that seen in the Merchant Navy class locomotives, and the boiler rings were adapted to lend the lagging the support needed.

[16] Livery of the Q1 Class was plain freight black, with Sunshine Yellow numbering on the cabside, and "Southern" lettering on the tender, shaded in green.

[17] Bulleid advocated a continental style of locomotive nomenclature, based upon his experiences at the French branch of Westinghouse Electric before the First World War, and those of his tenure in the rail operating department during that conflict.