This type is unusual in that it can operate on the Southern Region's 650 / 750 V DC third rail power supply, or an onboard diesel engine to allow it to be used on non-electrified routes.

The initial solution was to install simple tramway-type overhead wires to carry the 750 V supply in certain yards and add a pantograph on the locomotive roofs.

These locomotives also had a flywheel and pantograph, and were able to work in the more important freight yards across Kent that were fitted with the simple 750 V overhead wire system.

Although successful this system did require considerable extra cost, and maintenance, and still limited freight operations with the new locomotives to those goods yards fitted with the catenary.

This would be supported by adding a small diesel engine powerful enough to move reasonable freight loads at slow speed within goods yards.

[7] They differed slightly from the six earlier machines, most notably having an increased tractive effort as well as a higher maximum speed (90 mph as opposed to 80).

As the JA examples came in for overhaul over the years, the saddle buffers were also replaced making visual identification of the differing machines almost impossible from a distance.

The design parameter of the Class 73 was to provide a secondary main line electric locomotive to the then Southern Regions "mixed traffic" requirements, with the added ability to deliver, shunt and collect freight to and from yards adjoining the electrified network under diesel power.

To assume that the Class 73 was suitable to haul passenger or freight trains away from the electrified network with just a 600 hp diesel engine would be unrealistic.

In fact the use of the slightly more powerful Class 74 electro-diesels, with 650 hp on diesel, to haul parcels trains up Poole Bank and work freight trains around the West London Line to Acton, Brent and Willesden, resulted in repeated failures; this was, therefore, a major contributory factor to that class's early demise.

660V was phased out in line with pre-BR type electric multiple unit (EMU) withdrawals, the last EMUs incapable of working in passenger service on anything greater than 660V being the 4SUB Bulleid design.

Gaps in the third rail at complex pointwork or level crossings mean that a short electric locomotive such as Class 73 is liable to momentarily lose power when passing over.

The issue of arcing only became a problem when some of these locomotives were altered to work "Gatwick Express" services using modified Mark 2 coaching stock and 500 hp Gatwick Luggage Vans (GLVs), as 750V power jumpers between locos or units were banned on BR designs (the last EMUs to have such jumpers were the Bulleid designed 4SUBs).

As a result of removing the last bank of resistance on the Class 73 locos to make these trains accelerate more quickly, arcing increased.

Therefore, to reduce damage to other electrical equipment from the increased arcing, these particular locomotives had "flash guards" fitted on their bogies around the shoes.

The knuckle of this coupling could be lowered on a hinge (by removing a locating pin in its shank) to reveal the classic British hook.

The standard British buffer is needed to cope with the variable distance of chain-type couplings, to reduce buffeting and snatching behaviour.

Its shape is actually the floor section of a Pullman Gangway connection as seen on Buckeye fitted coaches (such as Mk1 types) or Multiple units.

In normal use the Class 73/1s were often seen working with Bournemouth line electric TC (non-powered) sets, which allowed such trains to be driven in Push-Pull mode.

Although technically possible, the Class 73/1s were not allowed to work in multiple or tandem with the Bournemouth line 4REP EMUs as this would exceed the "Current Limit Index" (CLI).

The two locomotives; 73118 and 73130, have additional coupling equipment fitted and were primarily used to rescue failed Eurostar sets, or to haul them over non-electrified routes.

When Eurostar moved its operations to the new Temple Mills depot and onto the overhead wiring of High Speed 1 in 2007, the Class 73 locomotives became redundant and were loaned to educational initiatives: 73130 went to RailSchool in East London and 73118 went to Barry Rail Centre in South Wales.

It was repainted in Fragonset's black freight livery, and was expected to be used on empty coaching stock moves associated with charter trains.

It was regularly hired to First GBRf from late 2004 as cover for their fleet and was based at c2c's East Ham Depot along with the Blue Pullman Rake.

The locomotive, formerly "Dave Berry", was renamed "Graham Stenning" after the company's Apprentice Manager, at Brighton Lovers Walk Depot on 11 December 2015.

[11] All existing mechanical and electrical components were removed prior to the re-fit, and the frontal appearance of the locomotives has been altered by the provision of light clusters and the installation of a more central location for the jumper cables.

[13] Merseyrail Electrics had a fleet of four Class 73/0 locomotives (numbers 73001/2/5/6), based at Birkenhead North TMD, for use on shunting and other departmental duties.

Subsequently, the locomotive was transited by rail to South West Trains Bournemouth Depot on long term hire.

Since 2006 Hornby have produced a representation of the prototype using the Lima tooling as part of their range in BR Green, whilst past examples have carried a variety of liveries.

[32] By 2007, Dapol had a broad range of Class 73 models for British N gauge, with examples in GB Railfreight and Gatwick Express liveries added at that time.