The Class 129 was a class of single-car Diesel Multiple Unit

Diesel multiple unit

A diesel multiple unit or DMU is a multiple unit train consisting of multiple carriages powered by one or more on-board diesel engines. They may also be referred to as a railcar or railmotor, depending on country.-Design:...

 built in 1955 for British Rail

British Rail

British Railways , which from 1965 traded as British Rail, was the operator of most of the rail transport in Great Britain between 1948 and 1997. It was formed from the nationalisation of the "Big Four" British railway companies and lasted until the gradual privatisation of British Rail, in stages...

. Only three were built by Cravens

Cravens

Cravens Railway Carriage and Wagon Company Limited was a railway rolling stock builder in the Darnall district of Sheffield, England. Cravens built many diagrams of coaching stock for the Pre-grouping Railway companies of Great Britain, the Grouped companies and for British Railways itself. They...

 and were introduced in 1958. The class was built for parcels traffic like the Class 128

British Rail Class 128

British Rail Class 128 was a class of diesel multiple unit, built for British Rail. Introduced in 1959, ten of the class were built by Gloucester Railway Carriage and Wagon Company, each with two 230 hp British United Traction engines. The class was built specifically for parcels, fitted out with...

. 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 British Rail Class 105

British Rail Class 105

The British Rail Class 105 diesel multiple units were built by Cravens Ltd. of Sheffield from 1956 to 1959. The class were built with a side profile identical to British Railways Mark 1 carriage stock, using the same doors and windows. None were selected for refurbishment...

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Departmental Usage

Single car unit No: RDB 975385 (formerly a Cravens parcels car No:M55997) was converted as a test bed for hydrostatic drive in 1980 and was known as 'Laboratory 9 Hydra'.

It was fitted hydrostatic transmission having the normal Leyland 680 six cylinder engine driving two Rexroth Hydromatic 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 400 bar.

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 scrapped by Vic Berry at Leicester.