The six principal classes of diesel locomotive that once made up the 'Type 4' classification - the 40, 44, 45, 46, 47 and 50 - were the survivors of a wider group that can trace its origins to the British Transport Commission's Modernisation Plan of 1955. Designating a power output of between 2,000 and 3,000 hp, the type once contained representatives of several non-standard and one-off prototype builds, including the Warship and Western diesel-hydraulics, which between them originally numbered over 100 examples. The scrapping, exporting or accidental writing off of the numerous Type 4 prototypes in the 1960s and early 1970s - with the exception of the ten Class 44 Peaks - left a cohort of over 900 diesel-electrics that became the real backbone of the BR fleet, including the most numerous single mainline class ever built in Britain, the 'Brush 4' - or Class 47, as it later became. This pictorial collection presents a wide-ranging selection of images of Type 4 locomotives from the late 1970s to the present day, photographed and compiled by Andrew Walker and John Walker with contributions from fellow photographer Vaughan Hellam.