They were officially designated "Curved Link 6-ft Passenger" due to the use of Stephenson valve gear which included a curved expansion link between the fore and back eccentric rods (earlier LNWR designs had used the Allan valve gear which had a straight expansion link) and the use of 6-foot (1.829 m) diameter wheel centres, which, together with 1+1⁄2-inch (38 mm) thick tyres gave a driving wheel diameter of 6 feet 3 inches (1.905 m).

[2] Ostensibly a mixed traffic design, they were the first locomotives with coupled driving wheels to be allocated for passenger duties on the LNWR.

They were designed by John Ramsbottom who had fifty built, all without cabs and with pierced driving wheel splashers.

The earlier locomotives also gained cabs, and all eventually had their splashers filled in.

The ten exceptions were transferred to the Civil Engineer's list, and these were withdrawn between 1914 and 1925.