As a diesel-powered variant of the British Desiros, the class 185 was created for the TransPennine Express. The order was placed in 2003 as part of a franchise between TPE parent company First and Keolis, which included the ordering of 56 three-car trains and the construction of associated maintenance facilities. Ultimately, only 51 trains were purchased, which were delivered in 2006 and 2007. Built at the former Uerdingen waggon factory, the vehicles replaced the Class 158 Sprinter units and the leased Class 175 Alstom Coradia.
The requirements for the vehicles included a top speed of 100 mph and at the same time good acceleration, since the area of operation was in a hilly landscape. The required performance was achieved through the use of a Cummins QSK19 with 750 hp per car and the power transmission via a hydraulic three-speed gearbox from Voith. These each drive both axles from one bogie and enable an acceleration of 1.1 mph per second.
Starting in 2007, Siemens and TransPennine Express tested a so-called “Eco-Mode” that automatically switches off individual engines depending on the driving situation. Because only two engines are running when driving downhill and one engine when shunting, a fuel saving of 7% and a 15% increase in the service life of the engines could be achieved. However, since this system led to problems, it was deactivated again for the affected trains and not pursued further.