This book is a comprehensive history of the four coupled tank engines absorbed by the Great Western Railway - locomotives of nine Broad Gauge companies, nineteen Standard Gauge companies, mainly in the South West which became part of the GWR between the 1870s and 1914, and a further eighteen companies, mainly in South Wales absorbed by the GWR in 1922 and 1923 at the formation of the 'Big Four' Grouping. The locomotives described and illustrated range from the 4-4-0 Broad Gauge saddle tanks of the South Devon and Bristol & Exeter Railways to the large 4-4-4 tank locomotives of the Midland & South Western Junction Railway, not forgetting the numerous and varied 0-4-0 pug saddle tanks of the Swansea Harbour Trust and the Powlesland & Mason company. The book includes thirty-two weight diagrams and nearly 200 photographs, many of exotic and rare locomotives.