All About the Bulleid 4DD

©John Atkinson and Mark Hickmott

Following the Second World War there was an increase in passenger traffic and solutions were being considered for the Dartford loop lines where the lengthening of trains would have been problematic due to the considerable infrastructure changes that would be needed to extend many of platforms along each route.

However, the physical constraints of the Southern’s loading gauge prevented the use of the ‘conventional’ design of double decked cars (as used overseas). But just prior to nationalisation in 1948 an innovative solution emerged from Oliver Bulleid and the Southern’s carriage works at Eastleigh for a double decked design of electric multiple unit.

Bulleid’s design achieved two levels through the interleaving of upper and lower level compartments along the length of each car; the upper level compartments being reached by a short flight of steps from the adjacent lower (platform height) compartment.

 Unit Construction

During the summer of 1949 two experimental Double‑Deck units were constructed at Lancing works, 4001 being completed in September and 4002 in October. The frames for these units were built at Lancing works and then taken to Eastleigh where some of the body construction was carried; the part-built coaches then being moved back to Lancing works for fitting out and painting.

Unit 4001 left Lancing works on 10th September 1949 and ran trials between Brighton and Haywards Heath before moving to Slade Green on 19th September 1949 for clearance tests in the suburban area. However, it returned to Lancing works on 17th to 22nd October 1949, 6th to 15th December 1949 and again 23rd December 1949 to 4th January 1950.

Unit 4002 was built with cast trailer wheels and left Lancing works 3rd October 1949 but returned to Lancing for adjustments and modifications between 6th December 1949 and 4th January 1950.

The cab end appearance was similar to the 4 SUB units although with a taller profile. Screw couplings with side buffers were fitted at unit ends, with the central buffer and three-link chain arrangement intermediately.

 Load Testing & Modification

When the units were ‘load tested’ at Lancing, the motor coaches failed with the frames going into reverse camber. To correct this, all four motor coaches had their roofs cut right across in the centre of the coach and the solebars were cut across the bottom flange and a vee cut up the web to the top flange.

The truss bars were then released by cutting through and the coach jacked-up until the requisite alignment was reached when the solebars and truss bars were then welded up and ‘dressed off’. Long stiffening plates were then fitted and welded over the cut areas. The cut in the roof was then welded-up and ‘dressed off’.

Both units entered service on 1st November 1949. They consisted of two motor brake seconds flanking two trailer seconds. The compartments were arranged alternately high and low, and the bodies were on standard 62′ 0″ underframes.

The motor coaches weighed 42 tons and seated 120 (55 seats on each level + 10 tip‑up seats on the upper level). At the outer end was the motorman’s compartment followed by the guard’s brake (which was 9′ 2″ wide) then the first of five upper level compartments interspersed with the five lower level compartments, the last of which was adjacent to the inner-end bulkhead of the coach. These coaches were to SR diagram number 2128. The doors to the guard’s brake were inset.

In the trailer coaches there were seven lower level compartments (the outermost ones adjacent to the end bulkheads of the coach) interspersed with six upper level compartments. These coaches were to diagram numbers 2020 and 2021; the difference being related to the buffing gear and jumper box arrangements in otherwise identical vehicles.

Throughout the units each compartment seated eleven; six on one side and five on the other with one of the centre seats being replaced by the steps into the neighbouring compartment. Upper level compartments also had two tip‑up seats each, one on each side facing inwards against the side of the coach where the door opening was normally situated in a conventional compartment. The trailer coaches therefore seated 156 (66 + 12 tip‑up on the upper level and 78 on the lower level).

The centre compartment on the lower level seated 12 as there was no gangway to an upper level compartment from this compartment. The three aside seats were on the nearside in each motor coach. However, in the trailers they were offside for the four compartments adjacent to the motor coach and nearside for the four towards the centre of the unit.

Each lower compartment also had conventional ¼ light windows each side of the door. Upper compartments also had normal size ¼ light windows and between them a larger one‑piece window where the doorway would be in a normal compartment. All the windows in upper compartments were sharply curved inwards towards the top as the window line was located across the normal cantrail curve of the body.

A passenger communication valve was provided above each door, there being none in the upper level compartments or a conventional cord arrangement.

Total unit weight was 136 tons and they were 257′ 5″ long and seated 552 passengers, giving a total of 1104 seats in the eight-car train. Units were designed for a maximum speed of 75mph. When new, the units were provided with the standard air whistle on cab ends, these were replaced by two-tone horns on the roof later in the units’ lives.


Seating differed from earlier units with thinner cushions only 3″ thick (the usual was 7″) and they were also narrower at 16½” as opposed to 18″ in conventional stock, and compartments were lit by specially made 70v filament lamps about 6″ long, those in lower compartments being built into the partitions above passengers heads. These were provided as there was insufficient clearance for a normal electric lamp, and they were often confused for a fluorescent tube.

Compartments were heated via the pressure ventilation system which was thermostatically controlled under overall control of the guard.

A number of grab rails were provided to assist any standing passengers and most internal surfaces were painted or varnished plywood panels.

Loading Gauge

To keep within the loading gauge the units had no commode handles or footboards and (for the same reason) had fixed windows with a pressure heating and ventilation system on the upper level. Equipment to power this ventilation system was located in a cupboard beneath the large centre windows of each upper level compartment, drawing air from below the train and supplying it beneath the feet of passengers in the upper level compartments.

Doors were flat, not curved as normal, to match the bodyside profile, each one having a conventional droplight window arrangement (with a small oval light above) as fitted to all‑steel 4 SUB units and later SR pattern EPB units.

These units were 9′ 0″ wide at waist level, the almost flat sides tapering inwards very slightly towards the cantrail level; body height was 9’ 7/8”. Overall height was 12′ 9″ (4 SUB units were 12′ 4½”) and as a result were restricted in passenger service to the lines between Charing Cross & Cannon Street to Gravesend Central by all four routes. Workings to other depots (mostly Selhurst or Lancing) were dealt with specially (i.e. via Special Traffic Notices).

Electrical Equipment

Electrical equipment included lightweight EE507 motors with EP control gear and Westinghouse EP self‑lapping brakes which were unique to the 4 DD units; as a consequence, these units could not work in multiple with any other type of unit. The EP brake equipment was recovered from the experimental equipment fitted to 6 PUL 3016 and 6 PAN 3034 in 1947/48.

These units also had the first application of the 27-way control jumpers on unit ends, replacing the separate lighting and control jumpers of previous types of SR unit; this being provided at the centre of the cab below the route indicator, which was a roller blind type from new (originally with larger style numbers).

Problems with mis-coupling the control jumpers led to them being moved to beneath the secondman’s observation light, leaving three small plates on the cab ends covering the earlier holes, these remaining visible on the units throughout their lives. Power jumpers were provided between units as in earlier designs.


Underframes were a deep girder type and together with special bolsterless bogies with smaller wheels than usual allowed a lower underframe level and more body space within the loading gauge. The solebars were fabricated in two different height sections, mostly 9″ below the passenger accommodation, but increasing to 15″ below the guard’s and motorman’s section to enable the buffing gear to be set at a conventional height, resulting in the side panelling stepping-up in this area and allowing fitment of a footboard alongside the cab and brake van doors.


Trailer bogies were to a novel design with side bearers transferring the weight directly to the bogie framing with no swing plank. The bogie wheelbase was 8′ 0″ and the BFB (Bulleid Firth Brown) type wheels were 3′ 0″ diameter. However, these bogies gave problems immediately with wheelsets cracking; the two units only running on 1st and 2nd November 1949 before returning to Lancing for further repairs and going back into service on 18th November 1949.

Late delivery of the new wheels from Firth Brown for unit 4001 had led to some improvisation and tyres of the correct size in store at Ashford were used, with new wheel centres welded together from matched segments and welded-up onto some old axles. Unit 4002 had cast BFB wheels from new, those on 4001 soon being changed at Slade Green. Further problems arose however and both units were extensively modified between 22nd November 1949 and 6th January 1950 when the train was out of use.

 Liveries & Depot Visits

When new the train was finished in malachite green livery with underframes and coach ends painted black and the roof was silver grey, though this soon weathered to a darker shade. The coach numbers were originally positioned on the bodysides’ left hand ends (between the compartment windows /to the right of the brake van doors); no ownership markings were applied.

Units received BR green at Selhurst; 4001 between 17th & 26th September 1951 and 4002 17th & 28th September 1951.

A darker shade of green was applied at Lancing during the units’ first major overhaul; coach numbers moved to a more conventional right hand end of the coaches and the BR Lion & Wheel coaching stock emblem appeared on the sides of each motor coach between the first and second low level compartments. Both entered Lancing works on 30th October 1957 with 4002 released on 6th February 1958 followed by 4001 on 14th February 1958.  The units returned to traffic thus, from 24th February 1958.

Small yellow panels were applied during their second major overhauls at Eastleigh, 4001 was there 4th January 1965 until 23rd April 1965 and 4002 there 9th February 1965 until 18th June 1965. Movement to /from Eastleigh normally took place via the Brighton line and along the coast to Fratton; the units then being loco-hauled to Eastleigh. However, in June 1965 unit 4002 returned via Guildford.

While the units were still in green livery, they received full yellow ends at Selhurst; 4001 between 5th & 24th January 1968 and 4002 5th & 25th January 1968.

During their final repaint (now into blue livery) at Selhurst (both between 14th & 26th September 1970) both units were officially renumbered 4901 and 4902 on 15th September 1970. This renumbering was to clear the 40xx number range for the forthcoming 4 PEP experimental sliding door units.

Depot visits for the units were as follows:

4001 4002
  In Out   In Out
Lancing 10-Sep-49 Lancing 3-Oct-49
Lancing 17-Oct-49 22-Oct-49
Lancing 6-Dec-49 15-Dec-49
Lancing 23-Dec-49 4-Jan-50 Lancing 6-Dec-49 4-Jan-50
Selhurst 17-Sep-51 29-Sep-51 Selhurst 17-Sep-51 28-Sep-51
Lancing 6-Jul-53 16-Oct-53 Lancing 6-Jul-53 16-Oct-53
Selhurst 21-Oct-53 5-Nov-53 Selhurst 23-Oct-53 5-Nov-53
Selhurst 21-Nov-55 1-Dec-55 Selhurst 21-Nov-55 29-Nov-55
Lancing 30-Oct-57 14-Feb-58 Lancing 30-Oct-59 6-Feb-58
Selhurst 23-Nov-59 3-Dec-59 Selhurst 23-Nov-59 2-Dec-59
Selhurst 29-Jan-62 9-Jan-62 Selhurst 29-Jan-62 10-Feb-62
Eastleigh 4-Jan-65 23-Apr-65
Eastleigh 24-May-65 18-Jun-65 Eastleigh 9-Feb-65 18-Jun-65
Eastleigh 29-Nov-66 16-Dec-66
Selhurst 5-Jan-68 24-Jan-68 Selhurst 5-Jan-68 25-Jan-68
Selhurst 14-Sep-70 26-Sep-70 Selhurst 14-Sep-70 29-Sep-70

MBS 13001 of unit 4001 was slightly damaged (details unknown) about October 1966 and unit to Eastleigh 29th November 1966 for C5 repair, released 16th December 1966.

 In Service

Workings remained fairly constant over the years, with both units being based at Slade Green depot where all routine maintenance was carried out. Both units usually ran two trips from the Dartford area to London and back during the morning peak, one unit then retiring to Slade Green for maintenance if required; the other working a further trip to London solo then also running to Slade Green to attach to its sister and a further three round trips to London and back as 8-cars in the evening business period before berthing again at Slade Green.

The exact content of these diagrams varied slightly over the years and from about 1951 the units no longer split during the day and only worked in peak hours and the Saturday midday peak, though this ceased about 1959 and the units were thereafter usually restricted to Monday-Friday only operation.

After the initial bogie problems had been solved the train was a technical success, but was not seen as the answer to overcrowding on the Eastern Section suburban services. This was principally due to the extended time the train took to load/unload at station stops, as each door now served 24 seats as opposed to 12 in conventional trains.

Other unsatisfactory features were a higher incidence of passenger accidents when joining and leaving the train due to the absence of footboards and commode handles, and some passenger concerns about security, particularly in the upper compartments as the train emptied out.

Unit Formation

Unit formations were as follows with the completion date shown below the unit number, delivery to SR date and coach type (letter code) being shown below the number:

Diag. No. Code 2128 CC 2020 DD 2021 DD 2128 CC  
4001 13001 13501 13502 13002 Sep-49
4002 13003 13503 13504 13004 Oct-49


Despite the many non‑standard features, the two 4 DD units remained in traffic until 30th September 1971 and both units were officially withdrawn from 9th October 1971 having been ‘condemned’ on 4th October 1971 following their last service train (18:04hrs Charing Cross to Dartford via Bexleyheath) on 1st October 1971.

Both were stored for a while at Plumstead and electrically stripped at Slade Green before moving to Hoo Junction yard 13th November 1971, where unit 4901 and trailer 13504 from 4902 were scrapped by Smeeth Metals, unit 4901 being cut-up 17th June 1972 and 13504 on 25th January 1973.

The remaining vehicles from 4902 were sold 22nd February 1972 for preservation at the Ashford Steam Centre and hauled there on 7th March 1972. However, this centre closed amidst financial difficulties and trailer 15303 was scrapped there 15th August 1984 by agents for the creditors. However, both motor coaches survived with 13004 being moved to the Northampton Steam Railway at Pitsford (having spent a period in T W Ward’s scrapyard at Silvertown) and 13003 moved to a farm near Molash in Kent where there was no public access.

Attempts to fit conventional buffing gear to 13004 at Pitsford proved abortive and the coach remained there in a badly vandalised state until moved to the Northampton Ironstone Museum at Hunsbury Hill 4th June 1999. 13003 was moved back to the site of the former steam centre at Ashford during June 1997 then moved to Hope Farm, Sellindge about May 1999.

The New Start for the Sellindge 4DD In 2015 a group was setup by Mark Hickmott and the Late Ian Ross to work with the Owner, The Late Esmond Lewis Evans to help with preserving the 4DD for the future. The group now of 6 people ventured down to Sellindge on the 19th December 2015 to meet Esmond and to cover the Sellindge 4DD for the first time in decades. The group members were Mark Hickmott, Chris Hurst, Tim Hannington, Bernard Tilly, Richard Midwinter and John Atkinson. Bulleid 4DD Double Deck EMU Supporters Group. During the next couple of years the group had been working on the 4DD and clearing the site of general rubbish. The group now growing in size, made the decision to setup up a group structure and mission statement with the aim to secure the Sellindge 4DD and if possible secure the sister Motor Coach based at the NIRT. In August 2018, Esmond passed away and his estate was put in Probate. In July 2018, the Bulleid 4DD Double Deck EMU Supporters group purchased the Sellindge 4DD. Since then, the group, thanks to greatly appreciated donations have purchased a bespoke cover which cover the whole of the 4DD, 12 units of racking and a work bench. New locks and other workshop items. Unfortunately because of Covid 19, the planned work for the 4DD has stalled.

©Thanks go to John Atkinson for the technical info and history notes.

 Additional group history by Mark Hickmott.