British Rail Class 121 information

British Rail Class 121
*Bubble Car*
British Rail Class 121; Bubble Car
	A Class 121 at Reading in 1992
	Interior of 121032
In service	1960–present
Manufacturer	Pressed Steel Company
Order no.	30518 (DMBS); 30519 (DTS);
Family name	First generation
Replaced	Steam locomotives and carriages; GWR railcars
Constructed	1960–1961
Entered service	1960
Scrapped	1978–2011
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); DX201 (DMBS, by 1994);
Fleet numbers	55020–55035 (DMBS); 56280-56289 (DTS, as built); 54280-54289 (DTS, renumbered);
Capacity	65 (DMBS); 91 (DTS);
Operators	British Railways; Network SouthEast; Regional Railways; Silverlink; Railtrack; Network Rail; Arriva Trains Wales; Chiltern Railways
Depots	BR Bath Road; BY Bletchley; LA Laira; RG Reading; TS Tyseley;
Lines served	Aylesbury–Princes Risborough line; Lostwithiel – Fowey; North Cornwall Railway; St Erth - St Ives;
Specifications
Car body construction	Steel
Car length	64 ft 6 in (19,660 mm) (over body)
Width	9 ft 0 in (2,740 mm) (over body)
Height	12 ft 4+1⁄2 in (3,772 mm)
Doors	Slam
Articulated sections	Single car (2)
Wheelbase	46 ft 6 in (14.17 m) (bogie centres); 8 ft 6 in (2.59 m) (bogies);
Maximum speed	70 mph (113 km/h)
Weight	38 t (37 long tons; 42 short tons) (DMBS); 30 t (30 long tons; 33 short tons) (DTS);
Prime mover(s)	2 × AEC of 150 hp (110 kW) per DMBS; or; 2 × Leyland 1595 of 150 hp (110 kW) per DMBS;
Engine type	11.1-litre naturally aspirated Diesel
Cylinder count	6 (horizontal) per engine
Power output	300 hp (220 kW) (DMBS)
Transmission	Mechanical (DMBS)
HVAC	Oil burning air heater
Bogies	DD10 mk3 and mk4 (DMBS, one of each); DT9 mk4 and mk5 (DTS, one of each);
Braking system(s)	Vacuum
Safety system(s)	AWS (DMBS)
Coupling system	Screw
Multiple working	■ Blue Square
Headlight type	Fluorescent and tungsten
Track gauge	4 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.

^ ^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)
^ Marsden 1983, p. 88
^ ^a ^b Fox 1987, pp. 30–31
^ ^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.
^ ^a ^b Fox & Hughes 1994, p. 12
^ ^a ^b Hemming 1978, p. 12.
^ Heginbotham, Stephen (2010). Cornwall's Railways Remembered. Halsgrove. pp. 51–52. ISBN 978-0-85704-005-3.
^ "ROLLING STOCK". The North Cornwall Railway. Archived from the original on 11 April 2021. Retrieved 11 April 2021.
^ Vaughan 1983, p. 106.
^ Marsden 2011, p. 98
^ "Mechanical And Electrical Coupling Index". Rail Safety and Standards Board. Archived from the original on 21 December 2013. Retrieved 20 December 2010.
^ "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.

[TRC1-1] ^ ^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)

[Marsden1983-88-2] Marsden 1983, p. 88

[Fox87-3031-3] Fox 1987, pp. 30–31

[BRBDMU220-4] ^ ^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.

[Fox94-12-5] Fox & Hughes 1994, p. 12

[FOOTNOTEHemming197812-6] 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.

[FOOTNOTEVaughan1983106-9] Vaughan 1983, p. 106.

[Marsden2011-98-10] 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.

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