|Engine:||Napier T9-29 Deltic diesel|
|Power:||1, 100 hp (820 kW)|
The fleet was refurbished in 1963 and modernised with a 4 character headcode replacing the original headcode discs and gangway doors . They continued to serve though had high maintenance costs and passengers and crews found they had excessive noise and fumes in operation. With these disadvantages and being such a tiny fleet there was no way the Baby Deltics could survive the fleet rationalisation at the end of the 1960s and all were withdrawn from normal service by 1971. One survived with the Railway Technical Centre and hauled test trains until 1975  but was scrapped like the rest of the class. No Baby Deltics now exist though the Baby Deltic Project aim one day to built a replica.
|D5901 at Doncaster in 1959, photographer unknown|
 John Vaughan, Diesels on the Eastern (Ian Allan, 1982) p. 31
 Brian Haresnape, Early Prototype and Pilot Scheme Diesel-Electrics (Ian Allan, 1981) p. 72
 Haresnape p. 75
 Colin J. Marsden, 25 Years of Railway Research (OPC, 1989) p. 67