Throughout its existence the Southern Railway pursued a policy of expanding the electrification of their major routes using the 750-volt DC third-rail system. As British Railways planned to eliminate steam locomotives during the 1960s the now Southern region required a small fleet of locomotives to haul special passenger, parcels and goods trains. For services over the electrified sections of the network an electric locomotive was an obvious choice. However it was quickly realised some kind of auxiliary power source would be required for shunting and in sidings where electrification was not practical. The most successful solution was the class 73 electro-diesel, a locomotive delivering up to 1,400bhp on electric power but carrying a 600bhp diesel engine for use away from the 'third rail'.
Following the building of a prototype batch of 6 locomotives built at Eastleigh works and designated type JA, a production batch of 43 locomotives were ordered from English Electric designated type JB, In addition to their own driving controls and BR blue star multiple working system for working with other diesels these locomotives were also compatible with the Southern region EMU multiple working control systems. Another fitting possibly unique to the class was a brake control system offering air controlled vacuum and vacuum controlled air brake options, so a 73 could run between air and vacuum braked stock, most useful in allowing vacuum braked parcels vans to be added to air braked EMU trains on 'boat train' services.
The class 73s have proved highly adaptable, being able to power anything from engineers freight trains to Gatwick Express services and several are still in regular use on the Southern region, most with GB Railfreight.
The Dapol Class 73 features:
- Detailed body with etched grills and separately fitted handrails
- RP25.100 darkened wheels
- Metal sprung buffers
- 5 pole Super creep motor with twin brass fly wheels for controlled pulling
- power and incredible slow running speed
- All wheel drive and pick up
- Independent directional lights & cab lighting
- Accessory bag with optional fitted components