Close up showing two LMS tender passenger locomotives together with LMS and ex-LNWR freight locomotives. The locomotives are, from left to right, a LNWR 0-6-2T 'Coal Tank' with a LNWR 0-6-0 'Coal Engine' behind on the same road, an unidentified LMS 4-6-0 Patriot class locomotive, two LMS 0-6-0 4F locomotives and LMS 5XP 4-6-0 Patriot class No 5515 'Caernarvon' facing towards the shed. The name 'Coal Engine' and 'Coal Tank' derived from the fact that the former was because they were designed to provide the motive power required for coal trains and the latter because it was a tank engine version of the former. Designed by Francis W Webb, they were formally described as 17 inch Coal Engines, the 17 inch referring to the diameter of the cylinders. Many aspects of the locomotive's design reflected John Ramsbottom's final design: the 0-6-0 Saddle Tank, including the identical wheel diameter and cylinder dimensions, but the new locomotives had a larger, improved boiler. In February 1878, one locomotive of this class was built from scratch in 25½ hours.
The 17inch Coal Engine was the first new design of locomotive to be built by Webb since he became Chief Mechanical Engineer (CME) of the LNWR in September 1871. A policy of 'low costs' was in force at the LNWR, with running costs per engine mile reduced from 10¾d per engine mile in 1857 to 7¾d by 1871. The first 17in Coal was constructed in 1873, the first of five hundred locomotives to be built. Ernest L Ahrons is quoted as regarding the type as 'probably the simplest and cheapest locomotives ever made in this country', whilst OS Nock described them as 'splendid'. The Coal Tanks were a side tank version of Webb's standard 17 inch Coal Engine and were introduced in 1881. They had the same cheaply produced cast iron wheels and H-section spokes as the tender engines but with an added trailing radial truck supporting the bunker using two similarly but smaller cast iron wheels. In total some three hundred were built between 1881 and 1899.