The British Rail Class 12 is a diesel locomotive built primarily for shunting duties around London. This was the second batch of Southern Railway shunters based on the English Electric 6KT 350 hp (260 kW) diesel engine. The first experimental batch (BR numbers 15201–15203) were designed by Richard Maunsell of the SR in 1937 and were later classified D3/12. These locomotives were Oliver Bulleid's development of Maunsell's original design, but were significantly lighter. They featured Bulleid's distinctive BFB wheels, and incorporated a number of details from the diesel-electric shunters produced by the London, Midland and Scottish Railway 1936–39.[2] They were built at the BR Ashford Works over the period 1949–1952 and numbered 15211–15236. They later became Class 12, but no locomotives survived long enough to acquire Class 12 TOPS numbers.