The London, Midland and Scottish Railway had the largest stock of steam locomotives of any of the 'Big Four' Grouping, i.e. pre-Nationalisation railway companies in the UK. Despite early troubles arising from factions within the new company, the LMS went on to build some very successful designs; many lasted until the end of steam traction on British Railways in 1968. For an explanation of numbering and classification, see British Rail locomotive and multiple unit numbering and classification.