Class 73 [Updated]

Despite the fact that diesel locomotives often spend a fair amount of time operating along electrified routes it is unusual that British Rail only ever built 2 classes of electro-diesel locomotives that could operate both as electric or diesel locomotives. Both were based on BR's Southern Region of which the Class 73 is the only survivor [1]. A growing number have been rebuilt and upgraded in the last few years so they look set to remain in service for a long time to come.

The Class 73 is an electric locomotive designed to work with SR's 660-750v DC third-rail system. It also has a small diesel engine for operating on non-electrified lines or if the power is off. They are highly versatile locomotives that have served on a whole range of traffic in Southern England, being true mixed traffic locomotives they could be found on passenger and freight services. Their numbers were steadily reduced in the privatisation era.

Information
Number built: 49, 11 re-engineered
Built: 1962 1965-67, Re-engineering from 2013-16
Builder: BR Eastleigh / English Electric
Re-engineering by RVEL Derby & Brush Traction
Engine: English Electric 4SRKT Mk II diesel
EE542A or EE546/1B traction motors
Re-engineered examples with 2 Cummins QSK19 or 1 MTU V8 diesels
Power: 1, 420 hp (1, 059 kW) - Electric
600hp (447kW) - Original EE diesel
1, 500hp (1, 119 kW) - Cummins
1, 600hp (1, 194 kW) - MTU

In the last couple of years however there have been 2 separate re-engining efforts to create the rebuilt 73/9 sub-class [2] (at one stage it was considered creating a new Class 75 but would have cost more in administration and re-certification [3]). The work includes replacing the original EE diesel with a much more powerful motor and replacing worn electrical and mechanical components. Eleven have been re-engineered to date in 2 phases. The "Phase 2" Class 73s with MTU diesels have had their third rail equipment removed [4]. As virtually "new" locomotives they will likely serve with Network Rail and other operators for a long time to come (they are expected to last at least 25 years). A number have also been preserved.

Sub-class Details
73/0 Original prototype batch, originally to have been called the Class 72
73/1 Main production batch, higher power output and speed
73/2 Modified for Gatwick Express push-pull duties (coupled to the Class 488 and 489)
73/9 Re-engineered and upgraded examples
73 952 at Kidderminster SVR

GB Railfreight 73 136 at Clapham Junction
Sideways view of 73 952

[1] Colin J. Marsden, Traction Recognition (2nd Edition) (Ian Allan, 2008) p. 82
[2] "Projects", RVEL <http://www.rvel.co.uk>
[3] "Re-engineered/tractioned 73s", WNXX Forum <http://www.wnxxforum.co.uk>
[4] "Caledonian Class 73 contract nears end", Today's Railways UK, March 2016, p. 32