British Rail Class 35

British Rail Class 35

Infobox Locomotive
name = British Rail Class 35
powertype = Diesel-hydraulic

caption = Preserved D7017 at Minehead in 1979
roadnumber = D7000–D7100
nicknames = Hymek
builder = Beyer Peacock (Hymek) Ltd
builddate = 1961–1964
serialnumber = 7894–7938, 7949–8004
gauge = RailGauge|ussg|lk=on|al=on
primemover = Bristol-Siddley / Maybach MD870
transmission = Hydraulic. Stone-Maybach Mekydro type 6184U
whytetype = B-B
uicclass = B'B'
wheeldiameter convert|3|ft|9|in|m|3|abbr=on
minimumcurve =
trainbrakes = Vacuum
locobrakeforce = convert|57|LTf|kN|sigfig=3|abbr=on|lk=in
wheelbase = convert|36|ft|0|in|m|abbr=on
length = convert|51|ft|8+1/2|in|m|abbr=on
width = convert|8|ft|10|in|m|abbr=on
height = convert|12|ft|10|in|m|abbr=on
weight = convert|75|LT|sigfig=3|lk=on
topspeed = convert|90|mph|0|abbr=on
poweroutput = "Engine:" convert|1700|bhp|sigfig=3|abbr=on|lk=on
tractiveeffort = "Maximum:" convert|46600|lbf|kN|1|abbr=on
trainheating = Steam
axleloadclass = Route availability 6
multipleworking = Yellow Triangle
railroad = British Railways
retiredate = 1971–1975
The British Rail Class 35 is a class of mixed traffic B-B diesel locomotive with hydraulic transmission. On account of their Mekydro-design hydraulic transmission units, the design became known as the Hymeks.

The type was developed for the Western Region of British Railways, which had opted for lightweight locomotives with hydraulic transmission when allocated funds under the British Railways Modernisation Plan of 1955. One hundred and one of the class were built between 1961 and 1964 when it became apparent that there was a requirement for a medium power diesel-hydraulic design for both secondary passenger work and freight duties.

They were allocated to Bristol Bath Road, Cardiff Canton and Old Oak Common. None of the class was named. Withdrawal from service began in 1971, and by 1975 all had been withdrawn. Their early withdrawal was caused, primarily, by BR classifying the hydraulic transmission as non-standard. Four examples survived into preservation


The builder, Beyer Peacock (Hymek) Ltd, was a joint venture between Bristol Siddeley Engines| (BSE) (licensed to build Maybach engines), Stone-Platt Industries (licensed to build Mekydro transmissions) and the locomotive manufacturer Beyer, Peacock and Company. At the time they were built, the Hymeks were the most powerful diesel hydraulic locomotive operating with a single engine - the Maybach MD870. Unlike the higher-powered diesel-hydraulic Warship and Western locomotives in the Western Region fleet (with dual Maybach MD655 engines), the Hymeks were not based on an existing West German design.


When first built, the Hymeks were given a more elaborate livery than many of the contemporary British Railways diesel classes. The main body of the locomotive was the standard dark Brunswick green, but with a lime green stripe along the bottom of the bodywork. The roof was medium grey, and the finishing touch was to paint the window surrounds in ivory white. In the early 1960s, yellow warning panels were added to the lower part of the front ends, in accordance with BR's then-new policy. Following the corporate identity campaign and the change of name to British Rail plus introduction of the “double arrow” logo in 1964, some locomotives received all-over BR Rail blue with small yellow warning panels. This was quickly changed by the return of off-white window surrounds. The final variation was BR blue with full yellow ends, the yellow being extended around the cab side windows.

Operational service

The type was initially employed on secondary passenger services based around Bristol, such as Paddington to Hereford and semi-fast services to the west of England and Wales. Once they had proved themselves more than capable of handling these duties, they were also assigned to express Paddington-Cardiff-Swansea services, displacing King-class steam locomotives. These duties were heavier than they were designed for, and the Hymeks were displaced when Western and Brush type 4 locomotives became available to allow accelerated timings.

Hymeks also worked pickup freights throughout the Western Region as a mixed-traffic design and were used heavily on inter-regional passenger services. This latter often caused operational problems as they would often terminate in areas where there were no trained staff to handle the locomotive once the rostered crew had ‘booked-off’. To avoid these instances, the locomotive would invariably be dispatched back to the nearest Western Region tracks without delay. The Hymeks were capable of operating in multiple, but only with each other. The electro-pneumatic control system (coded “Yellow Triangle”) allowed only one trailing locomotive to be controlled (by one driver): some trains were operated by three locomotives (all at the front of the train), but in these cases only two locomotives were connected in multiple, the third having a separate driver.

Hymeks were used all over the Western Region on mixed traffic services from secondary passenger and parcels through express freight to ballast trains. They were common in all parts of the region from Paddington to Bristol/South Wales/Worcester/Hereford. They also worked to Birmingham and the West of England, but were rare West of Plymouth.

Hymeks were notably used in multiple (up to 3 locomotives) as bankers on the Lickey Incline, propelling mainly freight trains from Bromsgrove to Blackwell. In this case the transmission was "locked" in second to prevent gear changes at inappropriate speeds and loss of propulsion.


Prejudice against the Western Region's diesel-hydraulic fleet had been present in other divisions of British Rail ever since the designs were first ordered. The aim of the Modernisation Plan, and in particular the rapid conversion of the entire BR fleet to diesel and electric traction, had been to stem BR's financial losses thought to arise partially from the labour-intensive nature of steam locomotive use. Although steam was eliminated from mainline use by 1968, many unsuitable designs of diesel locomotive had been rushed into service in the rush to achieve steam-free operation. The National Traction Plan of 1967/8 decreed that designs proving unreliable, expensive to maintain or non-standard should be eliminated as quickly as possible in order to reduce the number of diesel classes from 28 to 15 by the year 1974. The engineering factions of the British Railways Board, the body that oversaw BR's operations from 1962 onwards, felt that all of the Western Region's diesel-hydraulic fleet should be counted as non-standard and should be withdrawn as quickly as possible. Despite the fact that the Hymeks were statistically the most efficient of the Western Region's diesel-hydraulic fleet in terms of reliability, the entire class was withdrawn between 1971 and 1975. They were replaced by class 37 diesel-electric locomotives made redundant in other regions as a result of line closures and general decline in rail-borne freight traffic throughout the 1960s.

Formal withdrawal was not the end for three locomotives: 7076 and 7096 continued to be officially in non-revenue stock for some years; while 7089 also continued, but renumbered as TDB968005 in the Departmental series.


Four locomotives survived to be preserved.

* D7017 - West Somerset Railway
* D7018 - West Somerset Railway
*:D7017 and D7018 have been fully restored to working order since withdrawal. They are currently undergoing repairs at Williton Shed, West Somerset Railway and are unavailable for traffic.

* D7029 - Severn Valley Railway
*:D7029 is still undergoing a major restoration, and recently moved from Old Oak Common shed, in west London, to the Severn Valley Railway for further restoration, before a planned return to service in BR blue.

* D7076 - East Lancashire Railway
*:D7076 survived, along with sister locomotive D7096, at the Railway Technical Centre near Derby, where they were used as dead loads for research purposes. Warship no. D832 "Onslaught" was additionally present at this site. Both Hymeks were in poor condition, however it proved possible to rebuild one by using the other as a donor locomotive. D7076 was therefore restored using parts from D7096 and carries the number D7096 internally in one driving cab as a nod to the donor locomotive, which was reduced to a shell and subsequently scrapped. As of March 2007, D7076 is the only preserved Hymek in operational condition.

Hymeks in fiction

A Class 35 Hymek was featured in The Railway Series books by Rev. W. Awdry (the original 'Thomas the Tank Engine' stories). D7101 (a fictional number), later named "Bear" on account of the growling noise made by his engine, was introduced in book No.23 "Enterprising Engines" as one of the good diesels. He however has not featured in the Thomas the Tank Engine and Friends TV Series.


*cite book | last = Reed | first = Brian | title = Diesel-Hydraulic Locomotives of the Western Region | publisher = David and Charles | date = 1974 | location = Newton Abbot | isbn =0-7153-6769-2
*cite book | last = Williams | first = Alan | coauthors = Percival, David | title = British Railways Locomotives and Multiple Units including Preserved Locomotives 1977 | publisher = Ian Allen Ltd | date = 1977 | location = Shepperton | isbn = 0 7110 0751 9

External links

* [ Diesel & Electric Preservation Group - owners of D7017 & D7018]

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