The LMS Fowler class 4P was the first in a series of 2-6-4T tank locomotives designed for long-distance commuter services. It was introduced in 1927 by Henry Fowler and formed the basis for derivatives by Stanier, Fairburn and Riddles. 125 of this class were build in Derby until 1934.

Their leading axle was of the same type as the one used on the Schenectady Moguls the Midland Railway received in 1899. They had a relatively high ratio of superheating and driving wheels of 5 ft 8 in which were good for speeds of 80 mph (129 km/h) and more. The last 30 locomotives built had more modern cabs with side windows and doors.

They were not only used for commuter trains, but also as bankers for passenger and goods trains on the Shap incline. They were withdrawn between 1959 and 1966 and none was preserved. In 2015, the LMS Patriot Project announced that they are planning to build a new member of this class when their No. 5551 “The Unknown Warrior” has been completed.