changes could be implemented without impacting much of the benefits of adopting the existing design. It was identified that this would result in a weight increase and thus a decreased power-to-weight ratio, but it was determined that the performance of the proposed DMU was only slightly lower, and it could achieve similar journey times across the intended cross-country routes as the Class 150. It was also found that, while there was a slight increase in fuel consumption due to the changes, the envisioned DMU had lower fuel consumption than locomotive-hauled trains and lower maintenance costs. Accordingly, it was decided to proceed with developing a detailed specification and issuing it to industry. Amongst the requirements listed in the issued specification was the explicit statement of the acceptability of the proven power trains of both the Class 150 and Class 151. Description The design of the Class 156 was relatively conservative in comparison to Metro-Cammell's earlier Class 151 design. Specific changes include the bodyshell being primarily composed of steel instead of aluminium; the deliberate decision was made to model the cab design on the earlier Class 150 was allegedly taken to ease union acceptance. Each coach is powered, being outfitted with a single six-cylinder Cummins NT855-R5 diesel engine coupled to a Voith T211r hydraulic transmission and Gmeinder final drive units. The Class 156 can achieve a top speed of . Construction of the welded bodyshells was subcontracted out; 118 by Procor Engineering of Wakefield, 60 by W.H. Davis of Mansfield, and 50 by Standard Wagon of Heywood. Aston Martin Tickford were awarded the interior fitout contract. The units were numbered 156401 to 156514. Each unit was formed of two powered vehicles, one of which contained a toilet. Individual vehicle are numbered as follows, where the final three digits of the vehicle number match the unit to which the vehicle belongs: 52401–52514: Driving Motor Standard Lavatory (DMSL) 57401–57514: Driving Motor Standard (DMS), containing an area for storing wheelchairs, bicycles, bulky luggage etc. Unlike the Class 150 units, the 156s have a single-leaf sliding door at either end of each coach. This reflected the expected longer journeys with fewer stops that the Class 156 was supposed to operate. As with the Class 150, all the doors are operable by passengers when released by the guard using one of two passenger door control panels; they are energised using a carriage key to turn a rotary