The locomotive exchanges of 1948, initiated by the fledgling British Railways, had far reaching consequences for the future locomotive stock of the industry, not least in the construction of new classes of steam traction. The first of the new classes to be ordered by the Railway Executive was for a new 4-6-2 Pacific design, incorporating the best in steam technology and with reduced maintenance requirements.
Robert Riddles, as the first Chief Mechanical Engineer of British Railways, drew heavily on his previous LMS designs in designing the new 4-6-2, with elements from Bulleid’s SR Merchant Navy design, blastpipe configuration from the GWR and LNER crank design being incorporated. Weight limits were kept within Bulleid’s Light Pacific margins and the result was a pleasing looking, very capable mixed traffic locomotive. The naming of locomotives under British Railways management was undertaken by a Locomotive Naming Committee of three senior railway officers, but it was Bishop Eric Treacy that suggested the name of Britannia for 70000, the first of the class, and it was by this name that the class was generally known.