The ‘73’ Electo-Diesels - in a class of their own?


Article written by Ian Crowder in 2010

Class 73 electro-diesel no 73129 has become part of the diesel fleet. Here is an introduction to this successful hybrid design which can trace its roots to the Southern Railway's inspired chief mechanical engineer, OVS Bullied, who had already made his mark as an innovator with the Merchant Navy and West Country pacifics.


The Class 73 concept is pretty much unique on the UK rail network in that it is equipped with two different power sources - power collection from the former Southern Region's 650/750v DC third rail system and also from the on-board diesel generator set. Hence the term 'electro-diesel' or ED.The Southern Railway first came up with the idea of dual-powered locomotives after the second world war. The intention was to overcome the disadvantage of using steam locomotives over long electrified routes but where short forays over non-electrified lines was required - for example in sidings. This followed Bullied's experiments with electric locomotives which were equipped with flywheel-driven 'boosters' to overcome loss of traction over gaps in the third rail that were wider than the length of the locomotive, for example over complex junctions (three of these were built, initially numbered CC1 to 3, later 20001-3 and then 70001-3 and designated class 70).


The then Southern Region continued to work on the concept and eventually placed an order for detail design and production of six electro-diesels in July 1959, using much the same electrical equipment as Bullied's first electric locomotives. Initially designated class JA, they emerged from Eastleigh works in 1962 and were numbered E6001-6 (later 73001-6). They were capable of developing 1,600hp in electric mode and 600hp when using diesel power. A great advantage was that power could be changed from one to the other at speed - the diesel could be started and stopped and the pickup shoes could be switched in and out, raised and lowered - all while on the move. They could also work in conjunction with other SR stock, including electric and diesel-electric multiple units, class 33 diesels and other classes of electric locomotive.


These first locomotives were very successful and reliable in traffic. A further 43 were subsequently built by Vulcan Foundry with only minor variations (and were designated JB), the last being delivered in 1967 - the last year of steam on the SR. The JBs had a top speed of 90mph, compared with the JA's 80mph. The JA's became class 73/0, and JB (of which 73129 is a member), 73/1.


They could mainly be found on freight, permanent way and parcels traffic but also occasionally on boat trains. Passenger use increased following the Bournemouth line electrification, when they worked with TC trailer stock before all the 4-REP powered multiple units were delivered. Later, when the 4-REPS were being withdrawn they were used once again in this role. But their first permanent passenger workings were with the Gatwick Express from Victoria.


E6036 before and after

During their life they have carried a number of different liveries. Initially turned out in green with a grey band (73/0's), with later ones (73/1's) in 'electric blue'; they have subsequently and variously carried many liveries including Network South East, InterCity, Gatwick Express, 'large logo' blue, departmental all-grey and 'Dutch' grey; Eurostar two-tone grey at North Pole depot, Mainline Freight blue, EWS red, GBRf blue and orange and even - for a few - Merseyrail yellow. One or two have even appeared in Pullman chocolate and cream, in which guise they have been seen hauling the VSOE Pullman stock.

A few of this useful, if uncelebrated, class remain at work, having seen well over 30 years' service.



The example on the GWR, no 73129, (pictured above by Michael Pember on the day of its arrival) is one of the few to have carried the full Network South East livery, blue with white, red and grey stripes. Following withdrawal it was removed to Booths scrapyard at Rotherham from where it was purchased and taken to the MOD base at Ashchurch for mechanical restoration. It is now resident on the GWR where it is largely used with the permanent way train, and was the first locomotive since the line was lifted to cross Stanway Viaduct on the Broadway extension. As of April 2010 the locomotive is undergoing repair and repainting into its original 'electric blue' livery.