text: The second was to allow locomotives under diesel power to move off and back onto third rail areas without risk of damaging "fixed" third rail pick up shoes.The Southern Region engineers, having done all the initial design work, set about building a prototype batch of six new "electro-diesel" locomotives at Eastleigh Carriage and Wagon Works during 1961–1962. The new locomotives had a respectable  on electric power, and an English Electric  diesel engine similar to those used in the Southern Region's diesel electric multiple Unit (DEMU) fleet. To improve versatility yet further, the locomotives were designed so that they could work in multiple with most of the Southern's electric and diesel multiple unit fleets as well as normal carriages and wagons. This meant the locomotives had to also be fitted with drop buckeye couplings and therefore the Pullman rubbing bar, and retractable buffers. The success of these prototype locomotives resulted in British Railways ordering a production batch of a further 43 locomotives from English Electric at the Vulcan Foundry in Newton-le-Willows. However minor technical differences prevented the prototypes (classified type "JA") working in multiple with the production examples (classified type "JB"). 