Since 1877, Francis Webb had the “Improved Precedent” built for the LNWR, but it still had to be run double headed for heavy express trains. So later George Whale developed the Precursor class, which was basically based on its predecessor and had a leading bogie. Since Webb had already developed a Precursor class, it is also referred to as “Whale Precursor”. A 4-4-2T tank locomotive called the “Precursor Tank” soon followed.

Between 1904 and 1907 130 locomotives were built. From 1913 onwards, the first ones were rebuilt with a superheater and received new cylinders with a diameter of 20.5 instead of 19 inches. The LMS took over the locomotives in 1923 and assigned them power class 3P. The remaining ones without superheaters were withdrawn between 1927 and 1936, the ones that were superheated until 1949.

Two developments were designed based on the Whale Precursor class. The first was the Experiment class, which Whale developed as a ten-wheeler in 1905. Whale's successor Bowen Cooke developed the “George the Fifth” class on the same basis, which still had the 4-4-0 wheel arrangement.