The Class 156 diesel multiple units were built in 1987 by Metro-Cammell at Washwood Heath, Birmingham. A total of 114x 2 car units were built to replace early first-generation DMUs and some loco-hauled trains on routes ranging from Anglia to Scotland.

The units have a similar design to that of the Class 150/2, with major differences including the longer body, and doors at the end of the carriage rather than towards the centre. Class 156s have a top speed of 75mph.

The largest operator of these units is ScotRail, where they can be found running commuter services out of Glasgow, as well as the iconic West Highland Line.