With high power and a relatively low weight (the Deltic was 32 tons lighter than a Class 45 but brought 800hp more to the table) the Deltic proved itself on top BR expresses and a production order for 22 was made to replace ex-LNER Pacifics on the East Coast Main Line . The production Deltics differed in appearance to the prototype and construction, one problem with the prototype had been its awkward size which limited its route availability, the production Deltics were somewhat slimmer and a bit longer .
|Builder:||English Electric Vulcan Foundry|
|Engine:||2 Napier Deltic 18-25 diesels|
|Power:||3, 300 hp (2, 460 kW)|
The Class 55s as they became known performed admirably on the ECML until being replaced by the High Speed Train in the late 1970s with a final withdrawal from service at the end of 1981. Although they still had a lot to offer the Class 55s were expensive to maintain and the small fleet made them uneconomic. Six Class 55s were preserved as well as the prototype, the diesels (along with the Western Class 52s) attracting a level of popularity and interest not seen since the end of steam.
This wasn't the end of the Deltic story however, in the mid-1990s the Class 55s made a return to National Rail service with 4 being mainline certified  and are often used for charter services and spot hire, even hauling freights.
|D9002 at Kidderminster SVR|
|55 019 at Kidderminster SVR|
|55 019 at Bewdley|
|55 019 approaches a train|
|Side view of D9002|
 Brian Haresnape, Early Prototype and Pilot-Scheme Diesel Electrics (Ian Allan, 1981) p. 11
 Haresnape, Prototypes p. 31
 Brian Haresnape, Production Diesel Electrics Types 4 and 5 (Ian Allan, 1984) p. 42
 Colin J. Marsden, Traction Recognition (Second Edition) (Ian Allan, 2008) p. 48