R. E. L. Maunsell's engineering career started in Ireland, where he graduated to the post of Chief Mechanical Engineer of the GSWR. He crossed to England just before the outbreak of the First World War to take up the same post on the SECR, where his first new design, a 2-6-0, was selected as a post-war standard class for Britain's railways (for at that time nationalisation was first seriously canvassed). With this design Maunsell introduced modern concepts to the locomotive practice of railways in the South and South East, and established the pattern of locomotive development for the Southern Railway, to which he was appointed CME at the 1923 Grouping.

An enterprising engineer, Maunsell was handicapped by lack of money and severe civil engineering restrictions in his efforts to re-equip the Southern with standard classes of modern locomotive. Nevertheless, he contributed several good-looking and efficient designs to the development of the British steam locomotive, his masterpiece unquestionably being the three-cylinder 'School', the country's most powerful and successful 4-4-0 ever.