In a diesel-mechanical multiple unit (DMU) the rotating energy of the engine is transmitted via a gearbox and drive-shaft directly to the wheels of the train, like a car. The transmissions can be shifted manually by the driver, as in the great majority of first-generation British Rail DMUs, but in most applications gears are changed automatically.

This SRC based DEMU was getting ready for departure from Santragachi towards Digha Flag Station. Photo by Sam on 29th Sept 2011. After the HWH-Digha line got electrified this DMU service discontinued. Now EMU locals runs between two stations.