Class 73

Class 73
Name	Class 73
Powertype	Electric / Diesel-electric
Builder	English Electric / British Rail Engineering Limited / Vulcan Foundry
Builddate	1962–1967
Totalproduction	49
Wheelarrangement	Bo-Bo
Gauge	4 ft 8+1⁄2 in (standard)
Primemover	English Electric 4SRKT or 6RK
Tractionmotors	English Electric
Topspeed	90 mph (145 km/h)
Tractiveeffort	45,000 lbf (200 kN)
Operator	British Railways / Network Rail / English, Scottish and Welsh operators

Class 73.

The Class 73 is a British electro-diesel locomotive introduced in the 1960s for duties on the Southern Region of British Railways. It combined third-rail electric capability with an onboard diesel engine, enabling operation on non-electrified sidings and relief workings while remaining compatible with Southern electric multiple units and infrastructure. The type became notable for its versatility on routes involving the Southern Railway third-rail network, frequently appearing on passenger, freight, and engineering trains across England and Wales.

Introduction

The Class 73 was conceived during a period of modernization when British Railways Board sought flexible traction to serve the Southern Region electrification that used a 750 V DC third rail. Influenced by earlier electro-diesel experiments such as the British Rail Class 74 prototypes and contemporaneous designs from English Electric and Vulcan Foundry, the Class 73 was intended to reduce dependency on banking locomotives around termini like London Victoria and Brighton while providing rescue capability for failed multiple units on the South Western Main Line and Brighton Main Line. The class entered service amidst infrastructure projects overseen by organizations including British Transport Commission and later operated under management by companies such as Network Rail and multiple post-privatisation train operators.

Design and Technical Specifications

The basic design featured a Bo-Bo wheel arrangement with a steel monocoque body and dual traction systems. Under the 750 V DC third-rail power pickup, traction motors supplied by English Electric delivered continuous power for mainline duties; when away from the third rail the on-board diesel engine — an English Electric 4SRKT derivative — provided auxiliary traction. Weight distribution and axle load adhered to route availability constraints relevant to structures managed by entities like the Ministry of Transport and regional civil engineering teams. Control systems incorporated multiple-unit compatibility developed to interact with rolling stock from manufacturers such as British Rail Engineering Limited and Metro-Cammell. Braking equipment conformed to standards set by the Railway Clearing House legacy and later regulatory frameworks under the Office of Rail and Road. Electrical protection and safety gear reflected practices promoted by British Rail Research Division.

Variants and Subclasses

Three principal subclasses emerged through service and modification. Early units were built by English Electric and Vulcan Foundry with original numbering aligned to pre-TOPS conventions; subsequent TOPS renumbering placed them into the 73xxx series managed by British Rail. Some locomotives underwent conversion to Class 73/1 specification to enhance reliability, while other examples were retrofitted with stronger diesel powerpacks to create a pseudo-Class 73/2 group for heavy engineering trains used by contractors such as Balfour Beatty and Amey. Private operators after privatisation refurbished selected examples for use by freight companies including DB Cargo UK and GB Railfreight, and heritage preservation groups like The Bluebell Railway and National Railway Museum acquired units for static and operational display.

Operational History

Initially assigned to depots serving terminals such as London Victoria, Brighton, and Portsmouth Harbour, the locomotives executed rescue and pilot duties, hauled parcels and newspaper trains for organizations like Royal Mail and John Menzies plc, and supported engineering trains during track renewals for contractors contracted by British Rail and later Network Rail. During the 1970s and 1980s they were visible on boat trains to Dover and on cross-London workings via the Windsor Line. After privatisation in the 1990s, Class 73 members worked with operators including Southern, Gatwick Express, and charter companies arranging excursions to destinations such as York and Bath. Their dual-mode ability kept them useful for depot movements at facilities run by Direct Rail Services and for light freight in regions where full electrification was absent.

Liveries and Preservation

Throughout their careers, these locomotives carried liveries applied by authorities and companies such as British Rail, Network SouthEast, Railfreight, and various post-privatisation operators. Examples wore British Rail blue with double arrow branding, the red and white Network SouthEast scheme, and company-specific colours used by operators including GNER and FirstGroup. Preservationists preserved several examples: heritage railways and museums including Bluebell Railway, Midland Railway – Butterley, and the National Railway Museum maintain operational and static examples. Private preservation trusts and groups have repainted units into historic liveries to represent service eras associated with British Railways Board and the subsequent corporate identities.

Accidents and Incidents

During decades of service some locomotives were involved in mishaps recorded by investigators from bodies such as the Rail Accident Investigation Branch precursor organizations. Incidents ranged from collisions at suburban junctions near Clapham Junction to derailments during engineering moves on the Southampton to London corridors. Several units sustained damage in incidents involving third-rail de-energisation or buffer overrun events at terminals including London Victoria and Brighton, necessitating repairs at works operated by British Rail Engineering Limited and contractor facilities belonging to companies like Wabtec and Alstom. Some serious collisions led to withdrawn examples that were later cannibalised for spares by heritage groups and operators such as Colas Rail.

Category:British rail locomotives