The BR diesel locomotive types, that under the TOPs renumbering scheme became Classes 44s, 45s, and 46s, are best known by their nickname of ''Peaks''. This is derived from the first ten locomotives being given the names of British mountains. These machines originated under the Modernisation Plan of 1955 as BR''s Type 4 design. The Class 45s and Class 46s had slightly more powerful engines compared to the Class 44s, with the Class 46s having Brush rather than Crompton Parkinson Ltd electrical equipment.The Class 45s became the main motive power on the Midland main line for many years, while the Class 46s were used heavily on cross country services between the North East and South West. The Class 44s were at first employed on the West Coast main line but were latterly were relegated to freight duties mostly being based at Toton depot in Nottinghamshire.This new study covers the three types from their design and inception through to withdrawal and preservation. It draws extensively on original source material from a number of archives, and is lavishly illustrated with over 200 black and white and colour photographs almost all of which are being published for the very first time.