Class 960, no. 960001 at Norwich on 31st January 2004. At the time, this unit was painted in Railtrack blue/green livery. It has since been reclassified as Class 901 unit no. 901001 and repainted in Network Rail yellow livery.

The Class 901 designation is used for two former British Rail Class 101 diesel multiple units converted for departmental use. They were reclassified from the Class 960 series in early 2004 by their owner Network Rail.

The two units are described below.

901001

This unit was converted in 1986 from a power-twin unit. It was rebuilt as an Ultrasonic Test Train, replacing the former-Derby Lightweight unit that was previously used for this task. The unit was substancially rebuilt, including new headlight clusters, sealing of many window, and later fitting of video and floodlight equipment for night-time use.

The unit also incorporates a heavily-modified former Class 432 4Rep driving motor vehicle, which is now an intermediate trailer.

 DM T DM 977391 (ex_51433) + 999602 (ex_62483) + 977392 (ex_53267) 

The unit was originally painted in a unique silver and grey livery. This was replaced by Serco red/grey in the mid_1990s, followed more recently by Railtrack Blue/lime green. Since the unit was reclassified from the Class 960 series in early 2004, the latest Network Rail yellow livery has been applied.

901002

This unit was converted in 1991, also from a power twin unit. It was rebuilt as test train "Iris 2", supplementing and eventually replacing the original "Iris" unit, which was a former-Derby Lightweight single_car unit.

 DM DM 977692 (ex_53222) + 977693 (ex_53338) 

Like 901001, this unit has carried various liveries, starting with a silver and grey livery similar to that carried by 901001. This was followed by Serco red/grey, Railtrack Blue/lime green, and most recently the latest Network Rail all-over yellow livery.