The small engine policy was partly the consequence of a difference in the background of senior managers. In most railway companies, the elite position was the design, construction and maintenance of locomotives. Bigger engines brought more prestige and allowed longer trains. In the Midland, the marketing department was paramount. They recognised that people wanted more frequent, shorter trains rather than an infrequent service. It concentrated on very light, very fast and frequent trains.
The Midland was blessed, in that George Stephenson had built its main lines with very shallow gradients. The LNWR had to cope with the hilly country north of Manchester. The Midland had also found it more efficient to use smaller, less fuel hungry locos, simply adding pilots or banking engines as necessary.
The Light Engine policy indirectly contributed to several rail accidents in the late-19th and early 20th centuries, such as those at Hawes Junction and Ais Gill. Accidents and less serious incidents were caused by several trains stalling due to insufficient power, even from multiple locomotives, and the much higher number of light engine movements needed over Midland lines to allow locomotives used for multiple heading operations to return to their depots. Both the accidents mentioned above happened in the north of England, on a line known for its steep gradients. On the majority of the Midland network, where frequency of service was more important than gradient performance, the Light Engine policy was used without issue. Only on the relatively few Midland lines with steep, long gradients did it cause these problems.
In 1907 the whole stock were renumbered in a systematic way, each class in a consecutive sequence, classes being ordered by type (passenger/tank/goods), power and age. After the grouping this system was adapted for the whole LMS
The Midland classified their stock into three classes numbered 1 to 3 with 1 the least powerful and three the most. Stock were also split into passenger and freight engines. Just before grouping class 4 was introduced. This system formed the basis for the subsequent LMS and BR classification systems.
Classes include:
Fowler claimed never to have designed a locomotive, but it is customary to attribute to a Locomotive Superintendent those designs produced during his term of office.
Five original Midland locomotives have survived, these being:
In addition, there are 13 engines of two classes built by the LMS to essentially Midland designs:
And two engines built by the Midland for the Somerset and Dorset Joint Railway:
Further, there are several more engines to later non-Midland designs built at Derby which have survived.