The Tadpole Units

The story of the Class 206 “Tadpoles” is a complicated tale of reforming;unprofitable lines and the background environment of the railways in the early 1960’s. To put the “Tadpoles” into context requires a step back in history; back to when the “North downs line” was first conceived. The line runs from Reading to Tonbridge and the first section from Reading to Reigate  was opened in 1849 with the stated objective of the Reading,Guildford and Reigate Railway company being to secure a route “from the West, North and Midlands to the channel ports” and this route was selected to bypass the inevitable congestion of running a line through the capital. The SER ( South Eastern railway) was one of the major players in the south at this time and the two companies shared several of the same directors.

​The SER had already completed the route from Redhill ( then known as Reigate junction)  to Tonbridge. You will notice from the stated objective above that there is no mention of providing passenger services along the route, only to create the route from the rest of the UK to the Channel ports. This goes some way to explain the  extraordinary route , particularly along the eastern section. The eastern part of the route is essentially a straight line from Redhill to Tonbridge with the result that there was no attempt to divert this route to the larger towns. This gives the bizarre situation of having stations such as Godstone ,being over 2 miles from the village. Nutfield, Edenbridge, Penshurst and Leigh stations are similarly isolated from the main residential locations and this situation was made worse when a more direct link from the capital to Dover was opened in 1868. All this  meant that the line has never been greatly profitable and has therefore never been the focus of great expenditure. Indeed the line was still using steam locomotives in 1964. The line was however invaluable to the inter-war aviators.

​The distinctive straight line of the track, with the assistance of the stations having their names written in large white letters on the roofs, meant that it was used as a navigation tool for aviators trying to get to Croydon aerodrome; the Heathrow of its day. Meanwhile,The Hastings line had seen the introduction of DEMU stock in 1957 but by the 1960’s, rail passenger numbers were nationally  in decline to the extent that losses had increased from £15 million in 1956, to £42 million by 1960. Within this scenario, enter Dr Richard Beeching and his report “The reshaping of British railways”. Part of his proposal that was never implemented, was to shut some of the stations on the North Downs line between Reigate and Guildford due to their unprofitability. In order to cut losses, local managers looked at cut backs. To stem losses on the Hastings line the service was reduced and this eventually rendered three complete Hastings units as spare.These units were the earliest “6s” type units, numbered 1002, 1003 and 1004.

​As identified in the basics section of this web site, these units were shorter ( initially built for the traditionally shorter steam hauled stock on this route) and more importantly for this story, narrower ( because of limited tunnel clearances on the Hastings line - see Hastings units under the basics section).Hastings units consisted of six carriages each with a motor unit at each end. This meant that six motor units ( the cab ends with the engine) and a number of trailer carriages were available for redeployment. The idea of using this stock to provide a service on the North Downs line was developed and seemed like a good idea to make use of this surplus stock. But there was a problem. The North Downs line could not justify a six carriage set, only a three. The six carriage Hastings units had a motor at each end as the engines  were just about sufficient to haul 3 carriages each.The three carriage Hampshire  and Oxted units did not need two engines and so were fitted with a Driving trailer at one end. A driving trailer coach consists of a drivers cab end, with the controls operating the engine in the carriage at the other end of the train. The problem was that as  the Hastings units did not require a Driving trailer, none would be available from this source of surplus stock. The solution was novel and was what led to these unique sets being  nicknamed “Tadpoles”. 

​Elsewhere on the network 6, 2EPB ( 2 carriage sets fitted with Electro Pneumatic brakes) electric units, and more importantly their driving trailers, were rendered spare through cut backs and collision damage. These cabs could be converted to run with the old Hastings units on the non-electrified line of the North Downs that could otherwise not justify the purchase of new stock. But there were problems. The control circuits between these two different types of unit were different as were the couplers and the position of the cables and pipe runs which had to be altered. Additionally, the axles were changed to mark 4 bogies with the use of roller bearings being preferred due to the anticipated high daily mileage ( 500 miles). The drivers power control also had to be altered as the DEMU  stock was fitted with a 7 position power control and the old electric stock used a 4 position system. The drivers controls therefore had to have several positions omitted ( notches 2,4 and 6) which could lead to some jarring and lurching from the diesel engines upon acceleration. 

​So there we have it. Six units consisting of  three carriages each,  which were made up of two narrow ex 6s Hastings stock carriages and the driving trailer from a  standard width,ex 2EPB stock. When viewed from the Hastings unit end, the 2epb unit at the back stood out as being appreciably wider giving the impression of a long tail and bulbous head, hence the nickname “Tadpoles”. The units had no first class accommodation and subsequently proved to have too little baggage accommodation for the large postal use on this line and so three of the five compartment partitions in the driving trailers were  removed to create more luggage space. The engines were up-rated to 600 bhp by the changing of the MS100 Napier turbo charger to the MS200 model that had already been fitted to the Hampshire and Oxted units. The English Electric  507d suburban electric motor that was fitted to the other DEMUs was replaced on these units  by the English Electric 507e which were better designed to deal with the large average daily mileages ( around 500 per day and 11000 per month)

​The units were subsequently renumbered as 1201 to 1206 and classified as 3R ( R for  Reading). The first test run on the Reading - Tonbridge line took place in December 1964 with first passenger use occurring on the 3rd January 1965 with the service consisting of  5 daily diagrams; Two starting at Reading; Two from Redhill and One at Tonbridge with one spare.  By 1966, most of the smaller stations on the line were un-staffed  and on board ticketing had to be introduced. As a result of this, the Driving trailers were usually locked on normal services to facilitate ticket issuing due to a lack of inter carriage corridors. The units were subsequently renumbered as class 206 under the tops system but kept the 1200 series of numbers displayed on the units. 

​Whilst not sounding particularly appetising, the hourly service increased passenger numbers to the extent that a faster limited stop service was introduced and this corresponded with greater passenger numbers across the whole network. Eventually problems with the ageing Hastings line based stock were becoming a problem and so in 1979, four of the Tadpoles were replaced with Western Region DMU stock. On the 12th May 1979 1201 and 1202 were disbanded and reformed as part of a five car Hastings set, 1002. In August 1979 unit 1204 was disbanded, quickly followed by 1203. However, the former 2epb driving coaches  saw a new lease of life,  being inserted into the 4 remaining 2h Hampshire units, thus creating the 3T (Tonbridge) sets and re-classified as class 204 - but thats another story......In March 1980 several Hastings motor units were damaged in a derailment at Appledore near Ashford ( see Incidents section on this website)  and so the remaining two tadpole units , 1205 and 1206 were quickly reformed into the existing Hastings fleet to replace the damaged units. Unit 1206 was later reformed using a 6L motor coach and worked the Reading - Tonbridge route until May 1981, before being  rostored to work the Hastings- Ashford route. 1206 remained as a spare unit until 1985.In May 1985, the Class 206 number was resurrected when Hampshire  unit 1113 was involved in a collision  just outside Victoria station and two of its carriages were  damaged and later scrapped.

​However, the unit  re-entered traffic in April 1986 with two carriages from a Hastings 6L unit and was later redesignated as  206101. It made regular appearances on the Marshlink line until October 1987, when it was  finally withdrawn from traffic. The unit is featured in the "Celebrity Unit" part of this website.The story of the Tadpoles seems to reflect the various ups and downs of the railway industry but does also seem  to provide evidence of at least one thing. The DEMU story is one of adaption and longevity and these units were the cornerstone of the non - electrified diesel services of the Southern railway for nearly 50 years, proving to be a sound and wise investment indeed.

Unit 1205 at Godstone station in 1970. The difference in width of the  2epb unit at the rear  is immediately obvious.

Picture courtesy of Tom Burnham

Sources ( accessed 20/03/2013)   (accessed 21/03/2013)  (accessed 07/08/2012) (accessed 22/03/2013)

Welch, Michael, 2005 “Southern DEMUs” Capital Transport Publishing ISBN 1854142879.

Welch, Michael, 2005 “Slam doors on the Southern” Capital Transport Publishing ISBN 1854142968

Robertson, Kevin and Abbinnett, Hugh, 2012," Southern Region DEMUs", Ian Allen publishing ISBN  9780711035119