To pull the most important express trains, the LSWR had three two-coupled locomotives built in Nine Elms in 1859, which were the first four-coupled standard-gauge engines in Great Britain with a driver diameter of seven feet. They bore the numbers 157 to 159 and were designated the Clyde class after the number 157 “Clyde”. Sometimes the class is called Lacy class after number 158. In the same year number 169 was built, which only had a dome on the firebox and none on the boiler barrel. The numbers 73 to 75 followed in 1864 and the numbers 95 to 100 in 1868. The last delivery is also known as the Centaur class, since it differed slightly from the older machines.

Schematic drawing of No. 157 “Clyde”

Locomotive Magazine, August 1903

According to Locomotive Magazine, they were Beattie's "favorite locos" and were therefore always kept in pristine condition. By the late 1870s, they pulled the heaviest express trains with ease. While the older machines disappeared from the scene as early as 1883, four of the six examples from the last delivery received new boilers between 1887 and 1890. They were also subject to multiple rebuilds, so that ultimately each locomotive was a one-off. These last ones were only phased out in 1899 and most of these had achieved a mileage of one million miles.