[15][16] One obligation under the franchise agreement was to introduce a new fleet of diesel multiple units, capable of operating at speeds up to 100 mph (160 km/h).

In addition, a depot at Cleethorpes was to be upgraded with refuelling and controlled emission toilet servicing facilities, and a train electric auxiliary supply.

[18] The franchise agreement specified a performance aim of 35,000 mi (56,000 km) per casualty,[19] with entry into service between March 2006 (first unit) and November 2006 (entire fleet).

The engine and torque converter were frame-mounted underfloor and suspended from the car body by flexible mounts.

Connections bridge the main 400 V AC and 110 V DC supplies across the cars of each train set.

[7] The design has a distance between each axle of 2.600 m (8 ft 6.4 in), with radial-arm primary suspension utilising steel coil springs with rubber elements; the secondary suspension is an air spring design supporting a bolster.

[6] The trains were designed for the steep hills encountered on the TransPennine routes;[38] as a result the units had a high installed power, unnecessary for most of the train's route sections, leading to low fuel efficiency relative to other DMUs.

[39] In mid-2007, Siemens and First TransPennine Express began a programme, named 'Eco-Mode', to improve the efficiency of the fleet.

[47][48] Following the introduction of the new Nova fleet in 2019 and 2020, it was originally planned and expected that 22 Class 185 units would return to Eversholt Rail Group.

[52] By 2007, increased use of some of the First TransPennine Express services (Sheffield, Manchester and Leeds) caused the operator to start lobbying the SRA for a fourth car to the three-car sets to increase capacity; however, the service overall was subsidised, presenting a cost barrier to further rolling stock leasing.

[53][54] By 2008, many of the peak-time trains operated by Class 185s on First TransPennine Express services were suffering chronic overcrowding.

[55][56] In June 2017, TransPennine Express began refurbishing Class 185s as part of its franchise commitments.

The design features a black background, the "ok" hand gesture, as well as a white bolt of lightning, followed by quotes surrounding the charity.