With the reopening in the mid 1980s of the Snow Hill Tunnel between Farringdon and the Blackfriars to Holborn Viaduct line, and the laying of track in 1986 with electrified third rail between those two points, cross London train services (as championed by the former Greater London Council) became a reality. To run these services dual voltage stock would be needed to accommodate 750v dc third rail running south of Farringdon and 25kV ac overhead running north. Electronic control systems had improved considerably since the last class of dual voltage units, the 1976 generation class 313, had been introduced and indeed the Southern Regions last class 455 unit had proven the concept of "chopper" (thyristor) control which was to be used on this new stock.

To commence the cross London service, which became branded "Thameslink" by Network SouthEast, an initial batch of 60 class 319 units was constructed. These used the same Mk3 EMU body shells as class 317 and 318 units, but with slightly increased passenger space in the driving cars by eliminating the vestibule behind the driving cab and without unit end gangways. However doors in the cab fronts were still required to enable evacuation of the units in the Metropolitan Widened Lines tunnels between Farringdon and Kings Cross. As a departure from normal Southern practice, and not learning from the lack of unit compatibility experienced with class 508 units whilst they were operating on the Southern region, high level MU jumper cables were not fitted. However a tidy looking cab front design was the result. These units were fitted with retention tank toilets, also because of the tunnels.

The initial batch units, class 319/0, were formed Driving Trailer Standard (DTS), Pantograph Motor Standard (PMS), Auxiliary (i.e. containing the motor-alternator set) Trailer Standard (ATS) and another DTS. Mileage accumulation on 319 units began on 1 March 1988 and in passenger service on some Southern Region internal services from the weekend of 9/10 April 1988. Full Thameslink service commenced in May 1988 and proved to be an immediate and considerable success, even far exceeding the expectations of the far sighted people who proposed the concept.

photograph by Colin Duff

photograph by Colin Duff

Following protests by holders of First Class season tickets who found they no longer had first class accomodation available to them, a further batch of 20 units containing first class accommodation was constructed for the longer distance Bedford and Gatwick Airport/Brighton services. Designated class 319/1 these units had a Driving Trailer Composite (DTC) in place of one DTS. The first recorded working of a 319/1 was on 23 October 1990 on the 1836 Victoria-West Croydon via Crystal Palace service and it worked a Thameslink service the next day. The full Bedford to Gatwick/Brighton service began on 21 January 1991.

In their early days the 319 units experienced an number accidents with their pantographs striking overhead structures whilst incorrectly raised on the Southern. This was found to be due to a wiring design fault - operating the overload reset whilst working in the 750v dc mode also disastrously raised the pantograph unless dc traction mode was first re-selected. Unit utilisation allowed use on internal workings both north and south of the Thames, but such workings increased on the Southern following a major revision of the Thameslink timetable cutting back on the number of destinations served south of the Thames.

photograph by David Lawrence

photograph by David Lawrence