Drummond designed the class T9 after it was found out that the firebox of the class C8 express locomotive was too small. He did not only increase the grate area from 20 to 24 square feet, but he also included cross-water tubes into the elongated firebox which were directly exposed to the heat of the fire. These contributed 165 square feet, in addition to the 148 square feet of the firebox plates. They increased the steaming rate by a considerable amount, but made maintenance very complicated. 66 were built between 1899 and 1901. 35 of these came from the LSWR's own Nine Elms works and 31 from Dübs. They gained the nickname “Greyhounds” due to their good acceleration and a top speed of 85 mph or 137 km/h.

The cross-water tube firebox was also used in the L12 “Bulldogs” which were the successors of the T9. Urie started to superheat the T9 in 1922 and completed the whole class in 1929. In this process he enlarged the smokebox, increased the cylinder bore from 18.5 to 19 inches, but removed the water tubes from the firebox. In 1947, 13 were converted to burn oil, but all these were withdrawn in the following year. After the founding of British Railways, the remaining locomotives were mainly used for lighter tasks in the West Country where they had a good route availability due to their low axle load. By 1959, 20 were still in service and the last one was withdrawn in 1963. The only one that was preserved is No. 30120, the original No. 120, and it is being owned by the National Railway Museum. It was running on the Swanage Railway and was stored since 2020, but is under overhaul again since late 2024.