SR Class 4Sub

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Southern Railway 4-SUB
British Rail Class 405
SR 4-sub 4101.jpg
4101 (prototype) in 1941
In service1941-1983
ManufacturerEastleigh Works
Number built185 units
Number preserved1 unit
Capacity368 - 386 Seats
Operator(s)Southern Railway and British Railways
Car lengthDMBSO: 62 ft 6 in (19.05 m)
TS & TSO: 62 ft (18.90 m)
Width9 ft (2.74 m)
Maximum speed75 mph (121 km/h)
Weight134 long tons (136 t; 150 short tons)
Traction motorsFour
Power outputEarly units: 4 x 275 hp (205 kW)
total 1,100 hp (820 kW)
Later units: 4 x 250 hp (190 kW)
total 1,000 hp (750 kW)
Current collector(s)Contact shoe
Braking system(s)Air (Westinghouse)

The Southern Railway (SR) and the British Railways (Southern Region) (BR(S)) used the designation Sub to cover a wide variety of electric multiple-unit passenger trains that were used on inner-suburban workings in the South London area. The designation 'Sub' was first officially used in 1941 to refer to newly built 4-car units. However, during the 1940s large numbers of earlier '3-Car Suburban Sets' were increased to four cars by the addition of an 'Augmentation' trailer, and became part of the 4-Sub category. The SR and BR (S) continued to build or else rebuild 4-car units to slightly different designs which became part of the 4-Sub Class. Many of these later examples survived in passenger use until late 1983, by which time British Rail had allocated to them TOPS Class 405.


3-Car Suburban Sets[edit]

In 1923, the Southern Railway inherited 84 3-car suburban electric multiple units from the London and South Western Railway (LSWR), dating from 1914.[1] These could be enhanced by 24 2-car trailer sets coupled between two units, creating 8-car formations. Over the next 18 years the SR acquired a further 516 3-car sets.[2] These were either new; rebuilt from steam stock inherited from the LSWR, the London Brighton and South Coast Railway (LBSCR) and the South Eastern and Chatham Railway; or rebuilt from LBSCR AC multiple units. Some rebuilt units had ‘torpedo style’ front ends, others had the newer, flatter, front ends used on the main-line stock introduced during the early 1930s. They were designated ‘3-Car Suburban Sets’ to differentiate them from main-line units, and were numbered between 1201 and 1800. They are sometimes referred to as ‘3-Sub units’, but this designation does not appear to have been used whilst they were in use.

The 3-car units ultimately proved to be inadequate for most trains and inconvenient as the trailer sets had no driving cabs and so had to be marshaled between two 3-car units. Therefore, many were augmented by the addition of a new trailer car and rebuilt as 4-Sub units between 1942 and 1948. The remainder of the 3-car units were withdrawn. The last 2-car trailer set was withdrawn in September 1948, and the last 3-car formation ran in 1949.[3]

4-Sub Units[edit]

Preserved 4-Sub unit 4732 with vertical ‘slab’ front end

In 1939, following the appointment of Oliver Bulleid as Chief Mechanical Engineer, the SR announced a new welded steel 4-car suburban unit with curved sides, seating six passengers across rather than the normal five.[1] The prototype unit, 4101, was not completed until 1941 due to the advent of the Second World War. This had composite (both First Class and Third Class) seating accommodation in one trailer car and domed cab roofs. A further nine units were built in 1944-5 with Third Class accommodation only. Twenty units were introduced from 1946 with a vertical, ‘slab’ front end, and Third Class accommodation only. The underframes were built at Lancing Carriage Works and the bodies at Eastleigh Works.

Rebuilt 4Sub Motor Car with ‘torpedo’ style front.

As mentioned above, between 1942 and 1948 many 3-Car Suburban Sets were rebuilt and enhanced by the addition of a new 'Augmentation' trailer car to create 4-Sub units. This was done by inserting new steel trailers rather than one of the existing trailer cars. The rebuilt units were renumbered between 4131 and 4249.

BR(S) continued to introduce 4-Sub units, both new and converted from existing units, until 1951.


The usual formation for the newly built units was to have a Driving Motor Brake Third (DMBT) car at each ends, with accommodation for 108 passengers in nine compartments, together with two Trailer Third (TT) cars between with ten or eleven compartments giving a total passenger accommodation for 456 in all four coaches. After the renaming of 'Third Class' to 'Second Class' in 1956 these became DMBS and TS respectively.) However some of the rebuilds had Trailer Composite (TC) cars. The earlier coaches provided compartments, whereas the post war newly built carriages tended to provide saloon or semi-saloon style accommodation to allow for more standing room. These new 'open' carriages were designated DMBTO or TTO.


Throughout their careers the 4-Sub units were used on the London suburban services of all three divisions of BR (S).

179 out of the 184 new units constructed between 1946 and 1951 were still surviving at the introduction of the TOPS computer system in the early 1970s but were expected to have limited working lives. Under TOPS all surviving units were allocated to Class 405, but divided into two sub-classes. Sub-class 405/1 included the former Southern Railway sets numbered between 4112 and 4387, and sub-class 405/2 included the former British Railways sets built after 1949 and numbered between 4601 and 4754. All had been withdrawn by 1983.

As withdrawals reduced the number of units, services were concentrated in certain areas so that by 1981 units working on the Central section were allocated to Selhurst Depot and were concentrated on London Bridge to East Croydon services, and on peak-time commuter services to/from Holborn Viaduct and Blackfriars. Units on the South Western section were allocated to Wimbledon Depot and were concentrated on services between Waterloo and Effingham Junction, Shepperton or Chessington, although all of the scheduled services were on weekdays.[4][5]


The rebuilt units began to be withdrawn in the late 1950s and all had been withdrawn by the end of the 1960s. Apart from a few accident damaged units, the newly built units began to be withdrawn in 1972, and had all been withdrawn by 1983.[6] Those units surviving in the early 1970s were designated as Class 405 under the TOPS computer system.

Departmental use[edit]

In 1972 a unit was converted for use transporting stores between Eastleigh Works and various Southern Region depots. Renumbered 024 the unit was based at Slade Green and followed a set route on a weekly schedule serving Stewarts Lane, Ashford, Hither Green, Slade Green and Selhurst.[7][8][9]

In 1974 unit 4367 was retired from revenue-earning service and converted for use as a mobile instruction train and was allocated to Ashford Depot. As part of the conversion the unit was renumbered 055.[10][9]

After withdrawal, some individual steel-bodied trailer vehicles were adapted for use in de-icing the third rail and were fitted with spraying and scraping equipment. These vehicles were renumbered ADS70050/1 and ADS70086/7 and were used in conjunction with stock having Electro-Pneumatic controls.[11] In 1977 some additional conversions for de-icing were made when 6 new 2-car units were created from 4-SUB Motor Brake vehicles. These were renumbered 004 - 009.[12]


A handful of Sub stock carriages have survived in preservation, thus:

  • Driving Motor car number 8143 (formerly of Sub unit 1293, later 4Sub 4308) is in the care of the National Railway Museum, York.
  • 4Sub unit number 4732, formed of DMBTO 12795, TT 10239, TTO 12354 and DMBTO 12796, was retained by British Rail after withdrawal from normal passenger service for use on special occasions. It was stored at the Electric Railway Museum, Warwickshire, after spending many years stored in the open at various locations, but has subsequently been moved to the One:One Collection site in Margate, Kent.[13][14]
  • Former Departmental Converted 4 Sub Carriage TT 10400 was stored at a private site, but was scrapped around 02/2020.
Unit number
(current in bold)
DMBTO TT TTO DMBTO Built Livery Location
1293 4308 8143 - - - 1925 Eastleigh SR Maunsell Green National Railway Museum
- 4732 12795 12354 10239 12796 1951 Eastleigh Southern Green One:One Collection, Margate
- - - 10400 - - 1951 Eastleigh Network South East Finmere

History of individual units[edit]

Unit Numbers Type Introduced Formation Notes
989-1200 - 1920–1937 Various Two-car Sub Trailer sets. Converted from LSWR, SECR and LBSCR steam stock and LBSCR AC electric stock. Disbanded between 1941 and 1948, some cars used to augment 3-car Suburban to 4Sub.
1201–1284 3-car Suburban 1914–1917 DMBT+TC+DMBC Built by London and South Western Railway, their numbers E1-E84, ex-steam stock. Most augmented to 4131-4171 and 4195-4234 series in 1942–1948.
1285–1310 1925 DMBT+TC+DMBT Western Section (London to Guildford & Dorking) units, new-build, short frames. Augmented to 4300-4325 series in 1945–1946.
1401–1495 1925–1926 Eastern Section units, ex-SECR steam stock. Most augmented to 4431-4594 series in 1946–1949.
1496–1524 1925 Eastern Section units, new-build, standard frames. Augmented to 4326-4354 series in 1945–1946.
1525–1534 1926 Eastern Section units, ex-SECR steam stock. Most augmented to 4431-4594 series in 1946–1949.
1579–1599 1932–1937 Ex-LSWR steam stock. Most augmented to 4401-4594 series.
1601–1630 1927–1928 Central Section units, ex-SECR steam stock. Most augmented to 4431-4516 series.
1631–1657 1928–1929 Central Section units, ex-LBSCR steam stock. Most augmented to 4517-4614 series.
1658–1701 1927–1928 DMBT+TC+DMBC Central Section units, ex-LSWR steam stock. Most augmented to 4172-4194 and 4235-4250 series.
1702–1716 1928 Central Section units, ex-LBSCR steam stock. Most augmented to 4517-4614 series.
1717–1772 1929–1930 Central Section units, ex-LBSCR AC electric stock. Most augmented to 4517-4579 series.
1773–1785 1930–1931 Ex-LSWR steam stock. Most augmented to 4517-4614 series.
1786–1796 1931–1932 DMBT+TC+DMBT Ex-LSWR steam stock. Most augmented to 4517-4614 series.
1797–1801 1932 Ex-LBSCR steam stock. 1801 later renumbered 1600. Some augmented to 4580-4614 series.
4101 4-Sub 1941 DMBT+TT+TC+DMBT Prototype new-build, steel bodied 4-Sub unit with domed cab roof.
4102-4110 1944–1945 DMBT+TT+TT+DMBT New-build, steel bodied 4-Sub units with domed cab roof.
4111-4120 1946 New-build, steel bodied 4-Sub units with vertical cab roof.
4121-4130 1946 DMBTo+TTo+TT+DMBTo
4131-4171 1942–1948 DMBT+TT+TT+DMBT Ex-3-car Suburban units, with additional ex-3-car Suburban trailer car.
4131-4132 1969 Second use of unit numbers. Formed from spare steel-bodied Sub cars, including those used in the 7TC unit.
4172-4194 1947–1948 Ex-3-car Suburban units, with steel-bodied Augmentation trailer.
4195-4234 1942–1948 Ex-3-car Suburban units, with additional ex-3-car Suburban trailer car.
4235-4249 1947–1949 Ex-3-car Suburban units, with steel-bodied Augmentation trailer.
4250-4257 1942–1948 Formed from a variety of spare Sub cars.
4277-4299 1948–1949 DMBTO+TTO+TT+DMBTO New build, steel-bodied 4-Sub units.
4300-4354 1945–1946 DMBT+TT+TT+DMBT Ex-3-car Suburban units, with steel-bodied Augmentation trailer.
4355-4376 1947–1948 DMBT-TT-TT-DMBT New build, steel-bodied 4-Sub units.
4377 1947 DMBT-TTO-TT-DMBT New build, steel-bodied 4-Sub unit, including prototype full saloon trailer car.
4378-4387 1948 DMBTO+TTO+TT+DMBTO New build, steel-bodied 4-Sub units.
4401-4594 1946–1947 DMBT+TT+TT+DMBT Ex-3-car Suburban units, with steel-bodied Augmentation trailer.
4601-4608, 4610/13/14 1947 DMBT+TT+TT+DMBT First use of unit numbers. Ex-3-car Suburban units, with steel-bodied Augmentation trailer.
4601-4607 1950 DMBTO+TT+TT+DMBTO Second use of unit numbers. New Driving Motor cars formed with trailers built between 1946 and 1948.
4617-4620 1972–1976 Formed from spare Sub cars built between 1946 and 1950.
4621-4754 1949–1951 DMBTO+TT+TT+DMBTO Most cars had new bodies on old frames, though some were entirely new build. 4667-4754 included an Augmentation trailer from withdrawn units.



  1. ^ a b Moody 1968, p. 88
  2. ^ The ABC of Southern Electrics. 1943. p. 12.
  3. ^ Moody 1968, p. 137
  4. ^ Rayner & Hogie 1981, pp. 13–16.
  5. ^ British Rail Locoshed book 1982. London: Ian Allan. 1982. p. 70. ISBN 0 7110 1198 2.
  6. ^ "4-Sub (Class 405)". Southern E-Group.
  7. ^ Motive Power Combined Volume. London: Ian Allan. 1981. p. 158. ISBN 0 7110 1127 3.
  8. ^ Rayner & Hogie 1981, p. 27.
  9. ^ a b British Rail 1979 Locoshed book. London: Ian Allan. 1979. p. 76. ISBN 0 7110 0931 7.
  10. ^ Williams & Percival 1977, p. 170.
  11. ^ Williams & Percival 1977, p. 172.
  12. ^ Motive Power Combined Volume. London: Ian Allan. 1981. pp. 157–158. ISBN 0 7110 1127 3.
  13. ^ Bailes, Kathy (7 June 2018). "Locomotive Storage Ltd in Margate welcomes the only surviving 4732 4-SUB unit". Isle of Thanet News. Retrieved 8 June 2018.
  14. ^ 4-SUB EMU gets permanent home Railways Illustrated January 2021 page 25


  • The ABC of Southern Electrics. Ian Allan. 1968.
  • Marsden, Colin J. (1983). Southern Electric Multiple Units; 1898 - 1948. Ian Allan. ISBN 0-7110-1253-9.
  • Moody, G.T (1968). Southern Electric 1909–1968. Ian Allan.
  • Rayner, Bryan; Brown, David (1983). The "4-Sub" Story. Southern Electric Group. ISBN 0-906988-09-8.
  • Rayner, B W; Hogie, J D (1981). Southern Region unusual train services 1981-82. Purley: Southern Electric Group.
  • Williams, Alan; Percival, David (1977). British Railways Locomotives and Multiple-Units including Preserved Locomotives 1977. London: Ian Allan. ISBN 0 7110 0751 9.