The 5600 Class 0-6-2 tank engines were designed by C B Collett, and were introduced in 1924. The class was originally designed to work in South Wales, to replace elderly locomotives 'inherited' at the Grouping, which took place in 1923, and were now worn out. Their design followed Great Western Railway practice, in that standard parts were used as far as possible. Included in Collett's innovations was a standard boiler which suitable for the 5600 and the locomotives which preceded it, complete with traditional copper-capped chimney and safety valves 'bonnet'. The 5600 class engines had the distinction of being the only locomotive of 0-6-2 wheel arrangement on the GWR. They were a tank engine of substantial size, weighing 62 tons 18cwt, and were 37ft 6ins long while the side tanks could hold 1900 gallons of water. One hundred of the class were built. Owing to pressure of work at the GWR workshops at Swindon, a number were built by outsidecontractors resulting in minor differences. In 1927 another hundred similar tanks were constructed, this was designated the 6600 Class, and was slightly hevier. All the locomotives that made up the two classes passed into nationalisation, and remaind in service until 1960, at which time they were withdrawn from service quite rapidly.