BTH Type 1 Bo-Bo – Happy 60th Birthday


This design was another of the ‘Pilot Scheme’ diesels that was not so much a failure in design, but a product of the lack of clear definition of requirements, and the reliance on the electrical industry in the UK to design, and deliver systems that functioned well on the 1950s and 1960s railway. They were too, it has to be said, very much at the mercy of Government policies that were in a state of flux, and driven by the rapidly changing economy of the times.

So, we have in the BTH, or AEI if you prefer, Type 1 diesel-electric locomotive intended for use primarily on freight traffics, and especially the wagonload, and non-bulk traffics.

BTH Advert 1958Between 1955 and 1965, the modernisation and re-equipment programme had resulted in many changes of direction, the very public trials and tribulations of comparing the different diesel engine and transmission systems, and the over optimistic electrification plans. At the same time, the massively increased competition from road freight transport companies saw dramatic reductions in the railways’ share of the market, and operating costs that were rapidly rising.

This in turn led to some very unwise, or not thought through decisions, under pressure from dwindling financial resources, and the appearance of too wide a variety of designs, and decisions made to bulk manufacture products that were unproven to the railway environment.

In the early days the 174 pilot scheme diesels were going to be built and tested before fleet orders were placed – this was abandoned only part way through. Some of the manufacturers were failing to transform from steam traction to diesel and electric, and the railways were forced to rely on a collection of – in particular – existing electrical industries, with limited rail experience.

AEI Type 1 DieselThe arrival of a contract with British Thomson Houston, for the 44 locomotives, designated Type 1, with a Paxman diesel engine, powering four DC traction motors and all the ancillary and control equipment would have been very welcome in those uncertain economic times. Did the Rugby factory have enough capacity, or indeed capability to build the locomotives – not really. As was the case with numerous other designs of the day, they subcontracted the design and manufacture of the mechanical parts such as bodies, running gear, bogies, etc., to others.

At the same time, the engineering and manufacturing industry in the UK was undergoing some upheaval too, with acquisitions and mergers, and the arrival of Associated Electrical Industries (AEI), bringing together Metropolitan Vickers and BTH back in 1928 didn’t benefit anyone. Although part of the AEI Group when the order for the new Type 1 was placed, BTH was still quoted on the stock exchange as a separate, rival company to the likes of Metro Vick and English Electric. BTH subcontracted most of the mechanical works to the Clayton Equipment Co. in Derby, and the Yorkshire Engine Co. in Sheffield.

They were ordered in 4 separate lots, the first 10 in 1955 under the Pilot Scheme, then 3 more orders in lots of 10, 17, and 7 in 1959, all equipped for multiple unit operation, and numbered from D8200 to D8243. They were intended for service on the Eastern Region, covering North East London to East Anglia

With the first 10 locomotives appearing between November 1957 and November 1958, Clayton Equipment supplied the bogies and superstructure to Yorkshire Engine Co. in Sheffield, where the frame construction and final assembly was completed. The remainder were built by Clayton at Hatton, Derbyshire, and delivered between October 1959 and February 1961.

Neither of these two companies had much experience of designing or building main line diesel locomotives, and were focussed on industrial and mining and battery driven products. The Yorkshire Engine Co. had built main line steam locomotives in the past, but Clayton’s of Derby were perhaps even more of a niche engineering company.

AEI Type 1 side viewSo, in 1957 – 60 years ago – the new British Railway Type 1 took its first steps – beaten to the number 1 spot of course, by English Electric/Vulcan Foundry design – the ubiquitous Class 20 as it is known today.

BTH Type 1 leading dimensions table

1964 Allocations

1974 AllocationsThe 1967 National Traction Plan resulted in the loss of many of these ‘Pilot Scheme’ types, but also made other mistakes, one of which included ordering the centre cab Class 17 locomotives from the Clayton Equipment Co. With BTH placing work with Clayton for the ill-fated Class 15 for the mechanical components, it does seem an odd thing to do, even more so considering that the later Clayton design was even more unreliable than the BTH design.

In the Class 15, the Paxman engine was a pressure-charged engine with sixteen 7inch x 7 ¾ inch cylinders in “V” formation, but generating a mere 800hp at what was essentially a high-speed engine, compared to many other around at that time. This engine proved to be a source of numerous problems in service, from general unreliability to excessive maintenance, and the poor visibility from the location of the cab didn’t help.

Class 15 2A major contributory factor for the withdrawal of the class was the decline in suitable freight working in the North East London to East Anglia area, and they were all withdrawn from operational service between April 1968 and March 1971. All except the four allocated for departmental service were scrapped by the end of 1972, and D8233 has been saved for preservation, and undergoing restoration on the East Lancashire Railway.

A lot of work has been done, and it is good to know that in its 60th anniversary year, an interesting design from BR’s early dieselisation years has survived.


Useful links:

The Class 15 Preservation Society

Class 15 logo