When Britain's railways were nationalised in 1948, a decision was taken to design new locomotives that would, hopefully, be cheap to run in the age of post-war austerity. This film looks in detail at many of the surviving types. Among them is the unique "Duke of Gloucester", the very last attempt at a passenger express locomotive. More successful were the 9F freight engines, whose ten driving wheels made them some of the best load pullers ever built, whilst many railwaymen regarded the Class 4 tank engine as perfection on wheels. This is a detailed study by professional documentary filmmakers of these engines at work, and includes graphic footplate action and expert analysis.