The 15 locomotives built by Ashford Works for the SECR between August 1917 and December 1923 were numbered 810–824. The Royal Arsenal batch of 50 locomotives purchased by the newly formed Southern Railway from 1923 were numbered A825–A875; the numbers followed consecutively from the Ashford batch but with a prefix "A" to denote a locomotive allocated for overhaul at Ashford Works. The prefix was gradually applied to the SECR batch. From 1928, a new system was adopted where all Southern Railway locomotives were renumbered into one sequence. The SECR and Woolwich N class batches became Nos.  1810–1875. The final batch of 15 locomotives, built between 1932 and 1934, were numbered 1400–1414 from new.