British Rail Class 129
The British Rail Class 129 was a class of single-car Diesel Multiple Unit built in 1955 for British Rail. Only three were built by Cravens and were introduced in 1958. The class was built for parcels traffic like the Class 128. One unit (55997) survived into departmental service being named 'Hydra'. The driving ends of a Class 129 car bore a visible similarity to that of the Class 105, also built by Cravens. Departmental Usage. One unit, M55997, was converted as a test bed for hydrostatic drive in 1980, was renumbered RDB 975385, and named  Laboratory 9 ‘Hydra’. It was fitted hydrostatic transmission having the normal Leyland 680 six cylinder engine driving two Rexroth Hydramatic axial piston pumps. Each pump supplied fluid to a Volvo fixed displacement compact axle-end motor which drove the axle directly. The maximum system pressure was in the order of . This arrangement was only fitted to one bogie, the other one retaining its normal drive but with the cardan shaft disconnected. The unit was finally withdrawn in January 1986 and scrapped in August that year by Vic Berry at Leicester.