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{{Short description|Class of single-car diesel multiple units}}
[[Image:121020 at Bewdley.JPG|thumb|250px|right|Chiltern Railways operate a single [[British Rail class 121|Class 121]] "Bubble Car" on [[Aylesbury]] to [[Princes Risborough]] shuttles. Set 121020 is seen away from its normal haunts, at [[Bewdley]] on the [[Severn Valley Railway]] on 15th October 2004, whilst taking part in the ''Railcar 50'' event.]]
{{Use dmy dates|date=October 2020}}
{{Infobox train
| background = #0033cc;color:white
| name = British Rail Class 121<br />''Bubble Car''
| image = File:121L124.jpg
| imagealt =
| caption = A Class 121 at {{stn|Reading}} in 1992
| interiorimage = 121032 Interior.JPG
| interiorimagealt =
| interiorcaption = Interior of 121032
| stocktype =
| service = 1960–present<!-- Do not change to 2023 without a reliable source saying the Class 121 has been withdrawn by Network Rail -->
| manufacturer = [[Pressed Steel Company]]<ref name=TRC1>{{cite web|url=http://www.therailwaycentre.com/Recognition%20tech%20Data%20DMU/DMU_121.html|title=Class 121, 149|work=The Railway Centre|url-status=usurped|archive-url=https://web.archive.org/web/20050309225650/http://www.therailwaycentre.com/Recognition%20tech%20Data%20DMU/DMU_121.html|archive-date=9 March 2005}}</ref>
| ordernumber = {{ubl|30518 ({{abbr|DMBS|Driving Motor Brake Second}})|30519 ({{abbr|DTS|Driving Trailer Second}})<ref name=Marsden1983-88>{{harvnb|Marsden|1983|p=88}}</ref>}}
| factory =
| family = [[List of British Rail diesel multiple unit classes#First generation|First generation]]
| replaced = Steam locomotives and carriages<br>[[GWR railcars]]
| yearconstruction = 1960–1961
| yearservice = 1960
| refurbishment =
| yearscrapped = 1978–2011
| numberconstruction =
| numberbuilt = {{ubl|16 (DMBS)|10 (DTS)}}
| numberservice =
| numberpreserved = {{ubl|12 (DMBS)|2 (DTS)}}
| numberscrapped = {{ubl|4 (DMBS)|8 (DTS)}}
| formation = {{ubl|Single car (with trailer)|DMBS(+DTS)}}
| diagram = {{ubl|DQ221 (DMBS)|DS201 (DTS)<ref name=Fox87-3031>{{harvnb|Fox|1987|pp=30–31}}</ref><ref name=BRBDMU220>{{cite book| title = Vehicle Diagram Book No. 220 for Diesel Multiple Unit Trains (Railcars)| publisher = British Railways Board| location = Derby| date = 1982| at = DQ221, DS201| via = Barrowmore MRG| url = http://www.barrowmoremrg.co.uk/BRBDocuments/Book220Issue.pdf| access-date = 19 February 2016| archive-date = 21 January 2015| archive-url = https://web.archive.org/web/20150121172516/http://barrowmoremrg.co.uk/BRBDocuments/Book220Issue.pdf| url-status = dead}}</ref>|DX201 (DMBS, by 1994)<ref name=Fox94-12>{{harvnb|Fox|Hughes|1994|p=12}}</ref>}}
| fleetnumbers = {{ubl|55020–55035 (DMBS)|56280-56289 (DTS, as built)|54280-54289 (DTS, renumbered)<ref name=TRC1 />}}
| capacity = {{ubl|65 (DMBS)|91 (DTS)<ref name=BRBDMU220 />}}
| operator = [[British Rail]]ways<br>[[Network SouthEast]]<br>[[Regional Railways]]<br>[[Silverlink]]<br>[[Railtrack]]<br>[[Network Rail]]<br>[[Arriva Trains Wales]]<br>[[Chiltern Railways]]
| depots = {{ubl|BR [[Bristol Bath Road depot|Bath Road]]{{sfn|Hemming|1978|p=12}}|BY [[Bletchley TMD|Bletchley]]<ref name=Fox94-12 />|LA [[Laira Traction & Rolling Stock Maintenance Depot|Laira]]{{sfn|Hemming|1978|p=12}}|RG [[Reading TMD|Reading]]|TS [[Tyseley TMD|Tyseley]]<ref name=Fox87-3031 />}}
| lines = {{ubl|[[Aylesbury–Princes Risborough line]]|[[Lostwithiel and Fowey Railway|Lostwithiel – Fowey]]<Ref>{{cite book | last = Heginbotham |first = Stephen |title = Cornwall's Railways Remembered |publisher = Halsgrove |year = 2010 |pages = 51–52 |isbn = 978-0-85704-005-3}}</Ref>|[[North Cornwall Railway]]<ref>{{cite web |url= http://www.northcornwallrailway.co.uk/rollstock.html |title= ROLLING STOCK |website= The North Cornwall Railway |access-date= 11 April 2021 |archive-date= 11 April 2021 |archive-url= https://web.archive.org/web/20210411213311/http://www.northcornwallrailway.co.uk/rollstock.html |url-status= live }}</ref>|[[St Ives Bay Line|St Erth - St Ives]]{{sfn|Vaughan|1983|p=106}}}}
| carbody = [[Steel]]<ref name=TRC1 />
| trainlength =
| carlength = {{convert|64|ft|6|in|mm|abbr=on}} (over body)<ref name=BRBDMU220 />
| width = {{convert|9|ft|0|in|mm|abbr=on}} (over body)<ref name=BRBDMU220 />
| height = {{convert|12|ft|4+1/2|in|mm|abbr=on}}<ref name=BRBDMU220 />
| floorheight =
| platformheight =
| entrylevelorstep =
| doors = Slam<ref name=TRC1 />
| art-sections = Single car (2)
| wheeldiameter =
| wheelbase = {{ubl|{{convert|46|ft|6|in|abbr=on}} (bogie centres)|{{convert|8|ft|6|in|abbr=on}} (bogies)<ref name=BRBDMU220 />}}
| maxspeed = {{convert|70|mph|0|abbr=on}}<ref name=BRBDMU220 />
| weight = {{ubl|{{convert|38|t|abbr=on}} (DMBS)|{{convert|30|t|abbr=on}} (DTS)<ref name=TRC1 />}}
| axleload =
| traction =
| engine = {{ubl|2 × [[Associated Equipment Company|AEC]] of {{convert|150|hp|abbr=on}} per DMBS|or|2 × Leyland 1595 of {{convert|150|hp|abbr=on}} per DMBS<ref name=BRBDMU220 /><ref name=Marsden2011-98>{{harvnb|Marsden|2011|p=98}}</ref>}}
| enginetype = 11.1-litre [[naturally aspirated engine|naturally aspirated]] [[Diesel engine|Diesel]]
| cylindercount = 6 (horizontal) per engine <ref name=BRBDMU220 />
| cylindersize =
| traction motors =
| poweroutput = {{convert|300|hp|abbr=on}} (DMBS)<ref name=TRC1 />
| tractiveeffort =
| transmission = Mechanical (DMBS)<ref name=BRBDMU220 />
| acceleration =
| deceleration =
| aux =
| powersupply =
| hvac = Oil burning air heater<ref name=BRBDMU220 />
| uicclass =
| aarwheels =
| bogies = {{ubl|DD10 mk3 and mk4 (DMBS, one of each)|DT9 mk4 and mk5 (DTS, one of each)<ref name=BRBDMU220 />}}
| brakes = [[Vacuum brake|Vacuum]]<ref name=BRBDMU220 />
| safety = [[Automatic Warning System|AWS]] (DMBS)<ref name=BRBDMU220 />
| coupling = [[buffers and chain coupling|Screw]]<ref>{{cite web|url=http://www.rssb.co.uk/RGS/Pages/MECHANICALANDELECTRICALCOUPLINGINDEX.aspx |title=Mechanical And Electrical Coupling Index |access-date=20 December 2010 |publisher=Rail Safety and Standards Board |url-status=dead |archive-url=https://web.archive.org/web/20131221005408/http://www.rssb.co.uk/RGS/Pages/MECHANICALANDELECTRICALCOUPLINGINDEX.aspx |archive-date=21 December 2013 }}</ref>
| multipleworking = <span style="color:blue;">■</span> Blue Square<ref name=TRC1 />
| light = Fluorescent and tungsten<ref name=BRBDMU220 />
| gauge = {{RailGauge|ussg}}
| notes =
}}


The '''British Rail Class 121''' is a single-car double-ended [[diesel multiple unit]]. 16 driving motor vehicles were built from 1960, numbered 55020–55035. These were supplemented by ten single-ended trailer vehicles, numbered 56280–56289 (later renumbered 54280–54289). They have a top speed of {{Convert|70|mph|4=0|abbr=on}}, with slam-doors, and vacuum brakes. The driving motor vehicles were nicknamed "Bubble Cars" by some [[railfan|enthusiasts]] (a nickname endorsed and made official by final passenger service operator [[Chiltern Railways]]).<ref>{{cite web|title=Retirement of the Class 121 "Bubble Car" – Last Day of Service on Chiltern Railways|url=https://www.chilternrailways.co.uk/news/retirement-class-121-bubble-car|publisher=Chiltern Railways|access-date=20 May 2017|date=9 May 2017|archive-date=14 April 2018|archive-url=https://web.archive.org/web/20180414091722/https://www.chilternrailways.co.uk/news/retirement-class-121-bubble-car|url-status=live}}</ref>
==Description==


The Class 121 is Britain's longest serving DMU, operating in passenger service for 57 years until 2017.
==Current Operations==


===Chiltern Railways===
==British Railways service==
[[File:W55033 at Colne Valley Railway 2.JPG|thumb|right|Preserved W55033 at the [[Colne Valley Railway]] in original green livery, with yellow "speed whiskers" (warning stripes) on the cab front. This unit differs from the rest of the class by the fitment of a small route indicator box above the centre window, like a {{brc|122}}, rather than a large headcode box.]]
The Class 121 vehicles were introduced in 1960 for use on the [[Western Region of British Rail]]. They were used on various lightly used branch lines in [[Cornwall]] including the {{rws|Looe}} branch, the branch lines off the main line in the Thames Valley including the [[Greenford branch line]], the [[Bridport Railway|Bridport branch line]] (closed 1975), and the [[Severn Beach line]] in Bristol. In 1978 all of the units were still allocated to Western Region depots.<ref>{{cite book |last1= Bowles |first1= LJ |last2= Mallaband |first2= P |title= Coaching stock of British Railways |publisher= [[RCTS]] |year= 1978 |page= 50 |isbn= 0-901115-44-4}}</ref>

Unlike the earlier (but similar) {{brc|122}}, which had a small destination indicator in the roof dome, Class 121 had a four-character headcode box in the roof dome, with the destination indicator inside the top of the centre cab window.

==Current operations==
{{Unreferenced section|date=April 2024}}
Upon privatisation of Britain's railways, the Class 121 fleet was only operated by one passenger company, namely [[Silverlink]], with several more units in departmental duties with [[Railtrack]]. Since [[Chiltern Railways]] retired its final two units in May 2017, there have been no examples left in revenue-making service.


However, [[Network Rail]] operates one Class 121 for various departmental roles. This has been reclassified as a {{brc|960}} departmental unit. Duties include route learning, video surveying of track and [[sandite]] application. In addition, the unit has been specially repainted in old BR blue livery. The unit is based at Aylesbury and was jointly used by Chiltern Railways for [[Route knowledge|route learning]].
===Newtork Rail===


==Past operations==
===Silverlink===
===Silverlink===
{{Unreferenced section|date=April 2024}}
[[Silverlink]] inherited a small fleet of four "Bubble Cars". They were mainly used on the [[Marston Vale line]] from [[Bletchley]] to [[Bedford]], as well as non-electrified lines in North London, such as the [[Gospel Oak to Barking line]]. The units replaced the previous fleet of {{brc|108}} and {{brc|115}} units, and were supplemented with a fleet of {{brc|117}} units cascaded from Thames Valley services.

The four units, nos. 55023/27/29/31, were based at [[Bletchley TMD|Bletchley depot]], where staff repainted set L123 (55023) into its original British Railways green livery. The others remained in obsolete [[Network SouthEast]] livery. In 1996, set L123 was withdrawn from traffic, and the other three were hired to [[First Great Eastern|Great Eastern]] for use on the [[Gainsborough line|Sudbury branch]]. These returned to Bletchley in 1997/98. Two of the units (121027 and 121029) were repainted into Silverlink's purple and green livery, and the third (121031) was repainted into Network SouthEast livery. The three units also received names from withdrawn [[British Rail Class 117|Class 117]] units.
* 121027 - ''[[Bletchley TMD]]''
* 121029 - ''[[Marston Vale line|Marston Vale]]''
* 121031 - ''Leslie Crabbe''

The units were replaced on Silverlink duties in 2001 by [[British Rail Class 150|Class 150 ''Sprinter'']] units which had been cascaded from [[Central Trains]]. The units have all since been transferred to departmental duties.

===Arriva Trains Wales===
{{Unreferenced section|date=April 2024}}
In 2006, 121032 was purchased by [[Arriva Trains Wales]] for use on the Cardiff Bay Shuttle. The unit has been repainted into Arriva colours and was hauled to Wales in June 2006 to enter service in July. The unit finally entered service on 16 August 2006 but was withdrawn 3 days later due to a major problem with the engine. The unit re-entered service on the Cardiff Bay line on 14 September 2006. In March 2013, following further extensive periods out of traffic, 121032 was finally withdrawn from service, due to a terminal engine fault. It was subsequently transferred to sister company Chiltern Railways and moved to Aylesbury at the beginning of 2014 and was later sold into preservation at the [[Wensleydale Railway]], moving north at the beginning of May 2015.

===Chiltern Railways===
[[File:121020 at Bewdley.JPG|thumb|right|121020 and 121034 at [[Bewdley railway station|Bewdley]] in 2004.]]
In 2003, Chiltern Railways reintroduced [[List of British Rail classes#1st Generation "Heritage" DMUs|"Heritage" diesel multiple units]] on its [[Aylesbury–Princes Risborough line|Aylesbury to Princes Risborough]] shuttle service. For this purpose, unit 121020 was purchased from [[Network Rail]], and heavily refurbished to allow it to operate passenger services. It was repainted into [[Chiltern Railways]] blue livery. The introduction of this unit allowed the release of a {{brc|165}} "Network Turbo" unit. This unit has been fitted with secondary (magnetic) door locking and other safety features, and thus was exempt from 30 November 2005 deadline for the withdrawal of all [[British Rail Mark 1|Mark 1 vehicles]]. Electronic destination indicators and internal passenger information systems were recovered from "Network Turbo" 165 032 at refurbishment and fitted to this unit. The external exhaust pipes were rerouted through the brake van area.

In May 2011, a second "Bubble Car" was reintroduced to regular service. Unit 121034, previously based at Tyseley Loco Works, was (less extensively) refurbished for use by the [[Birmingham Railway Museum]]. It is painted in BR Green livery and was also used on Aylesbury to Princes Risborough services, when required.<ref>{{cite magazine |last=Miller|first=Mark|title=Chiltern's latest trains are 50 years apart |magazine=[[Rail (magazine)|RAIL]] |issue=670|date=18 May 2011|page=11}}</ref>

Both units were additionally used on shuttles, as required, between Aylesbury and Quainton Road stations, on the occasion of events at the [[Buckinghamshire Railway Centre]].

In March 2013, Chiltern Railways acquired 121032 from [[Arriva Trains Wales]]. It sold the unit for preservation in 2015.

Chiltern's two final units were withdrawn from service on 19 May 2017, due to difficulties in obtaining spare parts given the age of the units, which were more than 50 years old. They were subsequently sold.<ref>{{cite news|title=The end is nigh for Chiltern's 'Bubble cars'|url=http://www.railmagazine.com/news/fleet/the-end-is-nigh-for-chiltern-s-bubble-cars|access-date=4 May 2017|work=Rail Magazine|date=10 April 2017|archive-date=20 April 2017|archive-url=https://web.archive.org/web/20170420155338/http://www.railmagazine.com/news/fleet/the-end-is-nigh-for-chiltern-s-bubble-cars|url-status=live}}</ref>

==Fleet details==
{{Unreferenced section|date=April 2024}}

===Active units===
Remarkably, considering the age of the fleet, the oldest unit (55020) was also the final unit withdrawn alongside 55034, which remained in daily service until 2017, whilst the youngest vehicle (55035) was the first to be dismantled. As of July 2014, 55021 (960021) and 55030 (960013) have also been scrapped.


==Preservation==
==Preservation==
Class 121s have proved popular for preservation on [[heritage railway]]s.


{| class="wikitable" style="text-align: center"
{| border="1" cellpadding="3"
|-
!align=left|Vehicle No.
!colspan=2|Vehicle no.
!align=left|Unit No.
!rowspan=2|Unit no.
!align=left|Vehicle Type
!rowspan=2|Vehicle type
!align=left|Location
!rowspan=2|Location
!align=left|Comments
!rowspan=2|Notes
|-
!Original
!Departmental
|-
|56287
|&ndash;
|L211
|DTS
|[[Epping Ongar Railway]]<ref>{{cite web |title=BR 56287 Class 121 DMU |url=http://www.cs.rhrp.org.uk/se/CarriageInfo.asp?Ref=2553 |website=The Railway Heritage Register Carriage Survey Project |access-date=17 February 2023}}</ref>
|
|-
|56289
|&ndash;
|L263
|DTS
|[[East Lancashire Railway]]
|
|-
|55020
|977722
|L120
|DMBS
|[[Bodmin and Wenford Railway]]<ref>{{cite web|url=http://www.preserved.railcar.co.uk/55020.html|title=55020|website=Railcar.co.uk|access-date=13 April 2018|archive-date=14 April 2018|archive-url=https://web.archive.org/web/20180414011316/http://www.preserved.railcar.co.uk/55020.html|url-status=live}}</ref>
|Departmental unit 960002 (1992–2002) then returned to passenger use until 2017<ref>{{Cite web|url=http://www.railcar.co.uk/data/vehicle/55020|title=55020 Details|website=Railcar.co.uk|access-date=13 April 2018|archive-date=14 April 2018|archive-url=https://web.archive.org/web/20180414010923/http://www.railcar.co.uk/data/vehicle/55020|url-status=live}}</ref>
|-
|55022
|977873
|L122
|DMBS
|[[Southall Railway Centre]]
|Departmental unit 960014<ref>{{Cite web|url=http://www.railcar.co.uk/data/vehicle/55022|title=55022 Details|website=Railcar.co.uk|access-date=13 April 2018|archive-date=14 April 2018|archive-url=https://web.archive.org/web/20180414011309/http://www.railcar.co.uk/data/vehicle/55022|url-status=live}}</ref>
|-
|-
|55023
|55023
|&ndash;
|L123
|L123
|DMBS
|DMBS
|[[Chinnor & Princes Risborough Railway]]
|rowspan=2| [[Chinnor and Princes Risborough Railway]]
|
|<small>Repainted into BR Green livery whilst based at Bletchley depot.
|-
|55024
|977858
|L124
|DMBS
|Returned to traffic 30 March 2019
|-
|55025
|977859
|L125
|DMBS
|[[Long Marston railway station#Long Marston Depot|MoD Long Marston]]
|Stored for use on the [[Bristol and North Somerset Railway]]<ref>{{cite web|url=http://www.preserved.railcar.co.uk/55025.html|title=55025|access-date=29 October 2016|archive-date=30 October 2016|archive-url=https://web.archive.org/web/20161030000540/http://www.preserved.railcar.co.uk/55025.html|url-status=live}}</ref>
|-
|-
|55026
|55026
|977824
|P126
|T005
|DMBS
|DMBS
|&ndash;
|[[Swansea Vale Railway]]
|Preserved at [[Swansea Vale Railway#Heritage railway|Swansea Vale Railway]] but scrapped in 2009<ref>{{cite web|url=http://www.preserved.railcar.co.uk/55026.html|title=55026|website=Railcar.co.uk|access-date=13 April 2018|archive-date=14 May 2021|archive-url=https://web.archive.org/web/20210514215733/http://www.preserved.railcar.co.uk/55026.html|url-status=live}}</ref>
|<small>Used as a sandite unit after retirement from normal traffic.
|-
|55027
|977975
|P127
|DMBS
|[[Ecclesbourne Valley Railway]]
|Previously [[Severn Tunnel]] emergency train 960302
|-
|55028
|977860
|L128
|DMBS
|[[Swanage Railway]]
|
|-
|55029
|977968
|L129
|DMBS
|[[Rushden, Higham and Wellingborough Railway]]
|Damaged by fire in May 2015.<ref>{{cite web|url=http://www.cs.rhrp.org.uk/se/CarriageInfo.asp?Ref=6158|title=BR 55029 Class 121 Single Unit DMU: Driving Motor Brake 2nd built 1960|access-date=10 October 2019}}</ref>
|-
|55031
|977976
|T002
|DMBS
|Ecclesbourne Valley Railway
|Previously Severn Tunnel emergency train 960303
|-
|-
|55032
|55032
|
|T009
|T003
|DMBS
|DMBS
|[[East Lancashire Railway]]
|[[Wensleydale Railway]]
|
|<small>Used as a sandite unit after retirement from normal traffic.
|-
|-
|55033
|55033
|977826
|T004
|T004
|DMBS
|DMBS
|[[Colne Valley Railway]]
|Colne Valley Railway
|Only bubble car to have carried Midline livery, when operating in the West Midlands PTE area.
|<small>Painted in experimental ''MidLine" livery.
<small>Used as a sandite unit after retirement from normal traffic.
|-
|-
|55034
|55034
|977828
|T005
|T005
|DMBS
|DMBS
|[[Locomotive Services Limited]]; Crewe<ref>{{Cite web |url=http://www.preserved.railcar.co.uk/55034.html |title=55034 |access-date=20 January 2021 |archive-date=7 July 2018 |archive-url=https://web.archive.org/web/20180707230504/http://preserved.railcar.co.uk/55034.html |url-status=live }}</ref>
|[[Birmingham Railway Museum]]
|Latterly operated by Chiltern Railways as 121034
|<small>Used as a sandite unit after retirement from normal traffic.
|}

==Order details==
{| class=wikitable
|+ Table of orders and numbers
! Lot No. !! Type !! Diagram !! Qty !! Fleet numbers !! Notes
|-
|-
| 30518 || Driving Motor Brake Second (DMBS) || 512 || 16 || 55020–55035 ||
|54285
|T004
|DTC
|[[Northampton Ironstone Railway Trust]]
|<small>Used as a sandite unit adter retirement from normal traffic.
|-
|-
| 30519 || Driving Trailer Second (DTS) || 513 || 10 || 56280–56289 ||
|54287
|L211
|DTC
|[[Colne Valley Railway]]
|align=left|-
|-
|54289
|L263
|DTC
|[[The Battlefield Line Railway|Battlefield Railway]]
|align=left|-
|-
|-
|}
|}


== Model railways ==
A [[OO gauge]] model of the Class 121 was produced by [[Lima (models)|Lima]] in 1998. The model was produced as unit 55035 in all-over rail blue livery and unit 55027 in Network SouthEast livery.<ref>{{cite magazine|title=Lima Class 121 diesel railcar|first=Chris|last=Leigh|magazine=[[Model Rail]]|pages=86–87|issue=4|date=Autumn 1998|location=Peterborough|publisher=EMAP Apex|issn=1369-5118|oclc=173324502}}</ref> In 2006, [[Hornby Railways]] launched its first version of the BR Class 121 in OO gauge.<ref>{{cite web|url=http://www.hornbyguide.com/class_details.asp?classid=151|title=Hornby BR Class 121|work=Hornby Railways Collector Guide|access-date=2 February 2020|archive-date=11 January 2020|archive-url=https://web.archive.org/web/20200111102048/http://www.hornbyguide.com/class_details.asp?classid=151|url-status=live}}</ref> This model was produced in BR blue and BR green, using the Lima body mouldings that Hornby had acquired.<ref>{{cite magazine|title=BR blue and BR green for the Class 121 railcar|magazine=Hornby Magazine|first=Mike|last=Wild|page=80|issue=1|date=April–May 2007|location=Hersham|publisher=Ian Allan Publishing|issn=1753-2469|oclc=226087101}}</ref> Since 2017 Hornby have produced a basic representation of the prototype as part of their Railroad range in BR Class 121 in BR Green.


==References==
{{Reflist|30em}}


===Sources===
*{{cite book|title=Multiple Unit Pocket Book|series=British Railways Pocket Book No.2|edition=Summer/Autumn 1987|year=1987|first=Peter|last=Fox|publisher=Platform 5 Publishing Ltd.|isbn=0906579740|oclc=613347580}}
*{{cite book|title=DMUs & Channel Tunnel Stock|series=British Railways Pocket Book No.3|first1=Peter|last1=Fox|first2=Barry|last2=Hughes|publisher=Platform 5|edition=7th|year=1994|isbn=9781872524597}}
*{{cite book|last = Hemming |first = R |title = British Rail DMU/EMU Allocation book |publisher = National Railway Enthusiasts Association |date = August 1978 |isbn = }}
*{{cite book|title=Motive Power Combined Volume|first=Colin J.|last=Marsden|publisher=Ian Allan|year=1983|isbn=0711012849}}
*{{cite book|title=Traction Recognition|first=Colin J.|last=Marsden|publisher=Ian Allan|edition=2nd|year=2011|isbn=9780711034945}}
*{{cite book|last = Vaughan |first = John |title = Diesels in the Duchy |publisher = Ian Allan |location = Shepperton |year = 1983 |isbn = 0-7110-1326-8}}

==External links==
{{Commons category|British Rail Class 121}}
*[https://www.railcar.co.uk/type/class-121/l The Railcar Association on Class 121s]


{{British Rail DMU}}
{{British Rail DMU}}

[[Category:British Rail diesel multiple units|121]]
[[Category:Pressed Steel Company multiple units]]
[[Category:Train-related introductions in 1960]]

Latest revision as of 23:27, 29 November 2024

British Rail Class 121
Bubble Car
A Class 121 at Reading in 1992
Interior of 121032
In service1960–present
ManufacturerPressed Steel Company[1]
Order no.
  • 30518 (DMBS)
  • 30519 (DTS)[2]
Family nameFirst generation
ReplacedSteam locomotives and carriages
GWR railcars
Constructed1960–1961
Entered service1960
Scrapped1978–2011
Number built
  • 16 (DMBS)
  • 10 (DTS)
Number preserved
  • 12 (DMBS)
  • 2 (DTS)
Number scrapped
  • 4 (DMBS)
  • 8 (DTS)
Formation
  • Single car (with trailer)
  • DMBS(+DTS)
Diagram
  • DQ221 (DMBS)
  • DS201 (DTS)[3][4]
  • DX201 (DMBS, by 1994)[5]
Fleet numbers
  • 55020–55035 (DMBS)
  • 56280-56289 (DTS, as built)
  • 54280-54289 (DTS, renumbered)[1]
Capacity
  • 65 (DMBS)
  • 91 (DTS)[4]
OperatorsBritish Railways
Network SouthEast
Regional Railways
Silverlink
Railtrack
Network Rail
Arriva Trains Wales
Chiltern Railways
Depots
Lines served
Specifications
Car body constructionSteel[1]
Car length64 ft 6 in (19,660 mm) (over body)[4]
Width9 ft 0 in (2,740 mm) (over body)[4]
Height12 ft 4+1⁄2 in (3,772 mm)[4]
DoorsSlam[1]
Articulated sectionsSingle car (2)
Wheelbase
  • 46 ft 6 in (14.17 m) (bogie centres)
  • 8 ft 6 in (2.59 m) (bogies)[4]
Maximum speed70 mph (113 km/h)[4]
Weight
  • 38 t (37 long tons; 42 short tons) (DMBS)
  • 30 t (30 long tons; 33 short tons) (DTS)[1]
Prime mover(s)
  • 2 × AEC of 150 hp (110 kW) per DMBS
  • or
  • 2 × Leyland 1595 of 150 hp (110 kW) per DMBS[4][10]
Engine type11.1-litre naturally aspirated Diesel
Cylinder count6 (horizontal) per engine [4]
Power output300 hp (220 kW) (DMBS)[1]
TransmissionMechanical (DMBS)[4]
HVACOil burning air heater[4]
Bogies
  • DD10 mk3 and mk4 (DMBS, one of each)
  • DT9 mk4 and mk5 (DTS, one of each)[4]
Braking system(s)Vacuum[4]
Safety system(s)AWS (DMBS)[4]
Coupling systemScrew[11]
Multiple working■ Blue Square[1]
Headlight typeFluorescent and tungsten[4]
Track gauge4 ft 8+1⁄2 in (1,435 mm)

The British Rail Class 121 is a single-car double-ended diesel multiple unit. 16 driving motor vehicles were built from 1960, numbered 55020–55035. These were supplemented by ten single-ended trailer vehicles, numbered 56280–56289 (later renumbered 54280–54289). They have a top speed of 70 mph (113 km/h), with slam-doors, and vacuum brakes. The driving motor vehicles were nicknamed "Bubble Cars" by some enthusiasts (a nickname endorsed and made official by final passenger service operator Chiltern Railways).[12]

The Class 121 is Britain's longest serving DMU, operating in passenger service for 57 years until 2017.

British Railways service

[edit]
Preserved W55033 at the Colne Valley Railway in original green livery, with yellow "speed whiskers" (warning stripes) on the cab front. This unit differs from the rest of the class by the fitment of a small route indicator box above the centre window, like a Class 122, rather than a large headcode box.

The Class 121 vehicles were introduced in 1960 for use on the Western Region of British Rail. They were used on various lightly used branch lines in Cornwall including the Looe branch, the branch lines off the main line in the Thames Valley including the Greenford branch line, the Bridport branch line (closed 1975), and the Severn Beach line in Bristol. In 1978 all of the units were still allocated to Western Region depots.[13]

Unlike the earlier (but similar) Class 122, which had a small destination indicator in the roof dome, Class 121 had a four-character headcode box in the roof dome, with the destination indicator inside the top of the centre cab window.

Current operations

[edit]

Upon privatisation of Britain's railways, the Class 121 fleet was only operated by one passenger company, namely Silverlink, with several more units in departmental duties with Railtrack. Since Chiltern Railways retired its final two units in May 2017, there have been no examples left in revenue-making service.

However, Network Rail operates one Class 121 for various departmental roles. This has been reclassified as a Class 960 departmental unit. Duties include route learning, video surveying of track and sandite application. In addition, the unit has been specially repainted in old BR blue livery. The unit is based at Aylesbury and was jointly used by Chiltern Railways for route learning.

Past operations

[edit]
[edit]

Silverlink inherited a small fleet of four "Bubble Cars". They were mainly used on the Marston Vale line from Bletchley to Bedford, as well as non-electrified lines in North London, such as the Gospel Oak to Barking line. The units replaced the previous fleet of Class 108 and Class 115 units, and were supplemented with a fleet of Class 117 units cascaded from Thames Valley services.

The four units, nos. 55023/27/29/31, were based at Bletchley depot, where staff repainted set L123 (55023) into its original British Railways green livery. The others remained in obsolete Network SouthEast livery. In 1996, set L123 was withdrawn from traffic, and the other three were hired to Great Eastern for use on the Sudbury branch. These returned to Bletchley in 1997/98. Two of the units (121027 and 121029) were repainted into Silverlink's purple and green livery, and the third (121031) was repainted into Network SouthEast livery. The three units also received names from withdrawn Class 117 units.

The units were replaced on Silverlink duties in 2001 by Class 150 Sprinter units which had been cascaded from Central Trains. The units have all since been transferred to departmental duties.

Arriva Trains Wales

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In 2006, 121032 was purchased by Arriva Trains Wales for use on the Cardiff Bay Shuttle. The unit has been repainted into Arriva colours and was hauled to Wales in June 2006 to enter service in July. The unit finally entered service on 16 August 2006 but was withdrawn 3 days later due to a major problem with the engine. The unit re-entered service on the Cardiff Bay line on 14 September 2006. In March 2013, following further extensive periods out of traffic, 121032 was finally withdrawn from service, due to a terminal engine fault. It was subsequently transferred to sister company Chiltern Railways and moved to Aylesbury at the beginning of 2014 and was later sold into preservation at the Wensleydale Railway, moving north at the beginning of May 2015.

Chiltern Railways

[edit]
121020 and 121034 at Bewdley in 2004.

In 2003, Chiltern Railways reintroduced "Heritage" diesel multiple units on its Aylesbury to Princes Risborough shuttle service. For this purpose, unit 121020 was purchased from Network Rail, and heavily refurbished to allow it to operate passenger services. It was repainted into Chiltern Railways blue livery. The introduction of this unit allowed the release of a Class 165 "Network Turbo" unit. This unit has been fitted with secondary (magnetic) door locking and other safety features, and thus was exempt from 30 November 2005 deadline for the withdrawal of all Mark 1 vehicles. Electronic destination indicators and internal passenger information systems were recovered from "Network Turbo" 165 032 at refurbishment and fitted to this unit. The external exhaust pipes were rerouted through the brake van area.

In May 2011, a second "Bubble Car" was reintroduced to regular service. Unit 121034, previously based at Tyseley Loco Works, was (less extensively) refurbished for use by the Birmingham Railway Museum. It is painted in BR Green livery and was also used on Aylesbury to Princes Risborough services, when required.[14]

Both units were additionally used on shuttles, as required, between Aylesbury and Quainton Road stations, on the occasion of events at the Buckinghamshire Railway Centre.

In March 2013, Chiltern Railways acquired 121032 from Arriva Trains Wales. It sold the unit for preservation in 2015.

Chiltern's two final units were withdrawn from service on 19 May 2017, due to difficulties in obtaining spare parts given the age of the units, which were more than 50 years old. They were subsequently sold.[15]

Fleet details

[edit]

Active units

[edit]

Remarkably, considering the age of the fleet, the oldest unit (55020) was also the final unit withdrawn alongside 55034, which remained in daily service until 2017, whilst the youngest vehicle (55035) was the first to be dismantled. As of July 2014, 55021 (960021) and 55030 (960013) have also been scrapped.

Preservation

[edit]

Class 121s have proved popular for preservation on heritage railways.

Vehicle no. Unit no. Vehicle type Location Notes
Original Departmental
56287 – L211 DTS Epping Ongar Railway[16]
56289 – L263 DTS East Lancashire Railway
55020 977722 L120 DMBS Bodmin and Wenford Railway[17] Departmental unit 960002 (1992–2002) then returned to passenger use until 2017[18]
55022 977873 L122 DMBS Southall Railway Centre Departmental unit 960014[19]
55023 – L123 DMBS Chinnor and Princes Risborough Railway
55024 977858 L124 DMBS Returned to traffic 30 March 2019
55025 977859 L125 DMBS MoD Long Marston Stored for use on the Bristol and North Somerset Railway[20]
55026 977824 T005 DMBS – Preserved at Swansea Vale Railway but scrapped in 2009[21]
55027 977975 P127 DMBS Ecclesbourne Valley Railway Previously Severn Tunnel emergency train 960302
55028 977860 L128 DMBS Swanage Railway
55029 977968 L129 DMBS Rushden, Higham and Wellingborough Railway Damaged by fire in May 2015.[22]
55031 977976 T002 DMBS Ecclesbourne Valley Railway Previously Severn Tunnel emergency train 960303
55032 T003 DMBS Wensleydale Railway
55033 977826 T004 DMBS Colne Valley Railway Only bubble car to have carried Midline livery, when operating in the West Midlands PTE area.
55034 977828 T005 DMBS Locomotive Services Limited; Crewe[23] Latterly operated by Chiltern Railways as 121034

Order details

[edit]
Table of orders and numbers
Lot No. Type Diagram Qty Fleet numbers Notes
30518 Driving Motor Brake Second (DMBS) 512 16 55020–55035
30519 Driving Trailer Second (DTS) 513 10 56280–56289

Model railways

[edit]

A OO gauge model of the Class 121 was produced by Lima in 1998. The model was produced as unit 55035 in all-over rail blue livery and unit 55027 in Network SouthEast livery.[24] In 2006, Hornby Railways launched its first version of the BR Class 121 in OO gauge.[25] This model was produced in BR blue and BR green, using the Lima body mouldings that Hornby had acquired.[26] Since 2017 Hornby have produced a basic representation of the prototype as part of their Railroad range in BR Class 121 in BR Green.

References

[edit]
  1. ^ a b c d e f g "Class 121, 149". The Railway Centre. Archived from the original on 9 March 2005.{{cite web}}: CS1 maint: unfit URL (link)
  2. ^ Marsden 1983, p. 88
  3. ^ a b Fox 1987, pp. 30–31
  4. ^ a b c d e f g h i j k l m n o Vehicle Diagram Book No. 220 for Diesel Multiple Unit Trains (Railcars) (PDF). Derby: British Railways Board. 1982. DQ221, DS201. Archived from the original (PDF) on 21 January 2015. Retrieved 19 February 2016 – via Barrowmore MRG.
  5. ^ a b Fox & Hughes 1994, p. 12
  6. ^ a b Hemming 1978, p. 12.
  7. ^ Heginbotham, Stephen (2010). Cornwall's Railways Remembered. Halsgrove. pp. 51–52. ISBN 978-0-85704-005-3.
  8. ^ "ROLLING STOCK". The North Cornwall Railway. Archived from the original on 11 April 2021. Retrieved 11 April 2021.
  9. ^ Vaughan 1983, p. 106.
  10. ^ Marsden 2011, p. 98
  11. ^ "Mechanical And Electrical Coupling Index". Rail Safety and Standards Board. Archived from the original on 21 December 2013. Retrieved 20 December 2010.
  12. ^ "Retirement of the Class 121 "Bubble Car" – Last Day of Service on Chiltern Railways". Chiltern Railways. 9 May 2017. Archived from the original on 14 April 2018. Retrieved 20 May 2017.
  13. ^ Bowles, LJ; Mallaband, P (1978). Coaching stock of British Railways. RCTS. p. 50. ISBN 0-901115-44-4.
  14. ^ Miller, Mark (18 May 2011). "Chiltern's latest trains are 50 years apart". RAIL. No. 670. p. 11.
  15. ^ "The end is nigh for Chiltern's 'Bubble cars'". Rail Magazine. 10 April 2017. Archived from the original on 20 April 2017. Retrieved 4 May 2017.
  16. ^ "BR 56287 Class 121 DMU". The Railway Heritage Register Carriage Survey Project. Retrieved 17 February 2023.
  17. ^ "55020". Railcar.co.uk. Archived from the original on 14 April 2018. Retrieved 13 April 2018.
  18. ^ "55020 Details". Railcar.co.uk. Archived from the original on 14 April 2018. Retrieved 13 April 2018.
  19. ^ "55022 Details". Railcar.co.uk. Archived from the original on 14 April 2018. Retrieved 13 April 2018.
  20. ^ "55025". Archived from the original on 30 October 2016. Retrieved 29 October 2016.
  21. ^ "55026". Railcar.co.uk. Archived from the original on 14 May 2021. Retrieved 13 April 2018.
  22. ^ "BR 55029 Class 121 Single Unit DMU: Driving Motor Brake 2nd built 1960". Retrieved 10 October 2019.
  23. ^ "55034". Archived from the original on 7 July 2018. Retrieved 20 January 2021.
  24. ^ Leigh, Chris (Autumn 1998). "Lima Class 121 diesel railcar". Model Rail. No. 4. Peterborough: EMAP Apex. pp. 86–87. ISSN 1369-5118. OCLC 173324502.
  25. ^ "Hornby BR Class 121". Hornby Railways Collector Guide. Archived from the original on 11 January 2020. Retrieved 2 February 2020.
  26. ^ Wild, Mike (April–May 2007). "BR blue and BR green for the Class 121 railcar". Hornby Magazine. No. 1. Hersham: Ian Allan Publishing. p. 80. ISSN 1753-2469. OCLC 226087101.

Sources

[edit]
  • Fox, Peter (1987). Multiple Unit Pocket Book. British Railways Pocket Book No.2 (Summer/Autumn 1987 ed.). Platform 5 Publishing Ltd. ISBN 0906579740. OCLC 613347580.
  • Fox, Peter; Hughes, Barry (1994). DMUs & Channel Tunnel Stock. British Railways Pocket Book No.3 (7th ed.). Platform 5. ISBN 9781872524597.
  • Hemming, R (August 1978). British Rail DMU/EMU Allocation book. National Railway Enthusiasts Association.
  • Marsden, Colin J. (1983). Motive Power Combined Volume. Ian Allan. ISBN 0711012849.
  • Marsden, Colin J. (2011). Traction Recognition (2nd ed.). Ian Allan. ISBN 9780711034945.
  • Vaughan, John (1983). Diesels in the Duchy. Shepperton: Ian Allan. ISBN 0-7110-1326-8.
[edit]
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