Henry Fowler, like LMS Chief Mechanical Engineers before him, was constrained by the company's desire to stick by its small engine policy. This policy was left over from the Midland Railway, the largest constituent company of the LMS, and resulted in some iconic steam designs such as the Fowler 3F Jinty, however ignored the reality that rail operations on a national level would bring.
Suddenly entrusted with lines running from London to Scotland, the LMS would not have large express engines that it could call upon such as the LNER's A1 Pacific. While this was a policy that Fowler would eventually overcome with his Patriot design, his 4P tank engine had its DNA within the policy.
The order for the Fowler tank engine was placed in March 1927, with the first engine being delivered from Derby works on the 9th December of the same year, number 2300. This new tank engine was a behemoth, the engine had a total wheelbase of 38ft 6in, with a driving wheel span of 16ft 6in resulting from the company's idea to reuse existing coupling rods measuring 8ft and 8ft 6in respectively. The 86 ton heft of the locomotive would be spread over the six driving axles, two trailing axles and the single leading axle.
The locomotives would find themselves spread around the LMS network, finding roles on both ends of the spectrum including operating on express suburban services around cities as well as operating banking duties around Shap summit.