The LMS and BR produced 645 Class 4 tanks from 1927 until 1951. The first batch were built from 1927 to 1934 to a Fowler design and built at Derby. The second batch were Stanier engines built from 1936 to 1943 and included a three-cylinder version; the final batch built from 1945 to 1951 were Fairburn engines built at Derby and Brighton.
