spare DTCL, and took the place of 79649 in 1957, when this was converted into a special saloon on diagram 565. It was later renumbered 999510 in the departmental saloon series and was eventually scrapped in 1981. In 1962 three of the power twin units were converted to power trailer units, when 79191–79193 were rebuilt as DTCL vehicles and renumbered 79633–79635. Powertrain Power Twins 79000+79500 to 79007+79507 Engine: Two BUT (Leyland) 125 bhp Transmission: Hydraulic, Lysholm-Smith (Leyland) torque converter Coupling code: Red triangle Remainder of the fleet Engine: Two BUT (AEC) 150 bhp Transmission: Mechanical Coupling code: Yellow diamond Departmental Use A number of cars from these units were subsequently transferred to departmental (non-revenue earning) use after withdrawal from normal service: 79018 + 79612 were rebuilt as an ultrasonic test train based at Reading, numbered 975007 + 975008. Replaced by unit 901001. 79900 was rebuilt as test coach "Iris", based at Bletchley, numbered 975010. Later transferred to the BR Research Division at the Railway Technical Centre at Derby, for its last few years in traffic, it was repainted into original BR Green livery. Replaced by unit 901002. 79185 was taken into departmental use for brake trials, numbered 975012. It was scrapped in 1970. 79250 and 79252 were taken into departmental use as staff messrooms, numbered 975013 and 975014. They were scrapped in 1978 and 1982 respectively. 79649, the inspection saloon mentioned above, took its place in the departmental series as 999510. Preservation Thanks to their extended life in departmental service, one 2-car unit and a single car unit survive in preservation on the Ecclesbourne Valley Railway, the former following a high-profile campaign. See also British Rail BEMU – a power-trailer two car EMU based on the Derby Lightweight DMU design. References External links Derby Lightweight Train-related introductions in 1954