In the late 1980s, the Network SouthEast division of British Rail, which operated the railway network in South East England, started to develop a new standard train, known as the Networker. To test out the technical arrangements for the Networker, a test train was used, converted from former Class 210 (the prototype 'Second Generation' Diesel Electric Multiple Units) carriages.

Initially the test unit was formed for trials on the 750V DC third rail system of the Southern Region, and was numbered 457001 (as with all Southern Region electric multiple units only the last four digits of the unit number were actually carried).

Later, the unit was altered to undertake trials on the 25kV AC overhead system used on electrified lines north of the River Thames. The unit was renumbered as Class 316 number 316999. To enable it to work on the AC electrification, a pantograph trailer from a Class 313 unit was inserted into the set, replacing one of the intermediate trailers. This spare vehicle (no. 67400) has since been incorporated into a Class 455/9 DC suburban unit, replacing a damaged TSO vehicle.

After the AC trials were complete, the set was returned to the Southern Region for storage, minus the Class 313 trailer, which returned to its previous formation. The two driving cars have now been preserved at the Coventry Railway Centre, while the remaining intermediate trailer has been scrapped.

The unit formation was:

Unit No.  DMSO    TSO     TSO     DMSO
7001      67300 + 67400 + 67401 + 67301

Vehicle details are shown below: