In 1941, Thompson became the LNER's Chief Mechanical Engineer (CME), and quickly initiated a plan of locomotive standardisation and modernisation. This was in stark contrast to his predecessor Gresly's policy of creating new locomotive types only when required. This suited the LNER's economic restraints, but did lead to many different types of locomotive with few common parts.
High on Thompson's standardisation plan, was a mixed traffic 4-6-0 type. Initially designated "Class B", they had been reclassified to Class B1 by the time the first locomotive No. 8301 Springbok had been completed in 1942. The pre-existing Class B1 were reclassified as Class B18 . The Thompson B1 would quickly become the most successful of Thompson's locomotive designs and a total of 410 were built by the LNER and British Railways (BR). The standard 4-6-0 design was intended to replace all of the 4-6-0s then in service
A total of 410 B1s were built, but only a few of these carried names. 274 B1s were built by the LNER. The first batch of ten were built before the 1946 renumbering, and were named after antelopes. The Springbok was re-numbered 1000.