Based on the class 240 locomotives, Matthew Kirtley developed the class 480. They had inner and outer frames, with the outer frames being curved. They later formed the basis for the class 700 with 17-inch cylinders. Johnson modernized them, enlarging the cylinders from 16.5 to 17 inches, and on some locomotives to 18 inches. In 1907, 205 of the original 232 machines were still in use. When the LMS was founded, the locomotives were grouped into power class 1F. Most locomotives were retired around 1930. 