The Class 47 was built between 1962 and 67 as the Brush Type 4 by both Brush Traction and British Railways Crewe works, eventually numbering 512 examples. The Class soon was to be seen working all types of trains across the network; although it was not without its problems, the most major resulting in the derating of the engine to 2580 bhp. Today, a small number of 47s remain in mainline service although generally on relatively light duties compared to that which they once worked, and further examples have entered preservation. By the 1990s and the privatisation of British Rail, considerable numbers were being withdrawn as life expired and many of those remaining were becoming increasingly unreliable. In 1997 the newly formed operator Freightliner decided to begin to address the problem by rebuilding twelve locos with secondhand General Motors engines (the Sulzer power unit being one of the biggest weaknesses) and alternators. The body and running gear remained the same and the locomotives were classified as 57. These were very successful, and remain in service today with DRS and West Coast Railways. Ross Taylor explores the history of these two fascinating classes through his compilations of excellent photography and annotation.