An electro-diesel locomotive is one that can operate either from an electrical supply, such as overhead catenary or (in this case) an energised third rail, or from an onboard diesel engine.

Buckeye couplers and high-level, or 'bagpipe', control & brake jumpers were fitted to facilitate working with other EP stock - especially TC units in push-pull mode.

They were intended especially for use on the boat trains to Southampton and Weymouth, as both routes included sections of non-electrified track and tramway along the public thoroughfare.

The elimination of the locomotive change (at either Eastleigh (for Southampton) or Bournemouth) was envisaged and their dual power capability would greatly accelerate timings and reduce operational complexity.

In August 1966, after initial strip-down and examination of E5016, engineers were forced to re-assess the build when it became apparent that the planned equipment changes could not be accommodated.

The second also housed standard equipment but additionally included the complex electronic control circuits that ultimately were the un-doing of the class.

Nevertheless, advances in power control technology – particularly solid-state electronics – allowed similar arrangements to be adopted reliably by other manufacturers and operators within ten years' time.

Until four additional 4-REP units were built in 1973 and 1974, Class 74 locomotives operated regular daytime passenger turns including Waterloo–Weymouth services as far as Bournemouth.

When in good order they were judged to be sprightly performers, and the electronic traction control meant that acceleration was equally solid on both diesel and electric power sources.

Although their multiple-working abilities allowed them to work with other locomotives of Classes 73 and 74, EP multiple unit stock, and any Blue Star fitted mainline diesel locomotive, multiple operations were exceptionally rare other than on the frequent balancing runs between their home depot of Eastleigh and their day-time out-stations of either Clapham Junction yard or Stewarts Lane depot, in readiness for night-time postal and newspaper trains from London Waterloo.

However, while the AC locomotives were needed to cover services on newly-electrified sections of the West Coast Main Line, the work for which the Class 74 fleet had been built was drying up.

The remaining seven members of the class were withdrawn en masse on 31 December 1977, whereupon they languished at Eastleigh depot for a period of many months before being sent for scrap.

It was given a light overhaul at Eastleigh before being towed to Derby, where it was eventually deemed to be unsuitable and subsequently scrapped at Doncaster Works in 1979.

[6] Silver Fox Models manufactures a 4 mm resin body kit to mount on a donor chassis, with the option to purchase a ready-to-run version.