After the Western Region had already ordered diesel-hydraulic locomotives, unlike the rest of the country, a more powerful locomotive was needed. This led to the production of 74 twin-engine machines with a total of 2,700 hp. With a top speed of 90 mph they occasionally reached 100 mph. They were given numbers from D1000 and are better known today under their later TOPS class 52. Like the other British diesel hydraulic locos they did not have one long life, so most were retired by 1976. As a result, none of them received the new number plate with the TOPS class. 