British Rail Class 121

British Rail Class 121 Bubble Car
L103 at Reading c. 1980s in all-over BR blue.
Interior of 121032
In service	1960–2017
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	Bletchley Reading Tyseley
Lines served	Princes Risborough to Aylesbury Line
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 (110 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
Cylinder count	6 (horizontal)
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, 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).

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

British Railways service

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 were built for use on the Western Region of British Rail. They were used on various lightly used branch lines, including the Looe branch line (and various other branch lines) in Cornwall, the branch lines off the main line in the Thames Valley, the Bridport branch line (closed 1975), the Severn Beach line in Bristol and the Greenford Branch Line in West London.

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

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

Silverlink

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 to Sudbury. 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.

• 121027 - Bletchley TMD
• 121029 - Marston Vale
• 121031 - Leslie Crabbe

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

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

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.

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, and will be sold.

Fleet details

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

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

Vehicle no.		Unit no.	Vehicle type	Location	Notes
Original	Departmental
56287	–	L211	DTS	Colne Valley Railway
56289	–	L263	DTS	East Lancashire Railway
55020	977722	L120	DMBS	Bodmin and Wenford Railway	Departmental unit 960002 (1992–2002) then returned to passenger use until 2017
55022	977873	L122	DMBS	Southall Railway Centre	Departmental unit 960014
55023	–	L123	DMBS	Chinnor and Princes Risborough Railway
55024	977858	L124	DMBS		Returns to traffic 30 March 2019
55025	977859	L125	DMBS	MoD Long Marston	Stored for use on the Bristol and North Somerset Railway
55026	977824	T005	DMBS	–	Preserved at Swansea Vale Railway but scrapped in 2009
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.
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
55034	977828	T005	DMBS	Chiltern Railways	Latterly operated by Chiltern Railways as 121034

Order details

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

In 2006 Hornby Railways launched its first version of the BR Class 121 in OO gauge. 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

Sources

• 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. {{cite book}}: Invalid |ref=harv (help)
• Fox, Peter; Hughes, Barry (1994). DMUs & Channel Tunnel Stock. British Railways Pocket Book No.3 (7th ed.). Platform 5. ISBN 9781872524597. {{cite book}}: Invalid |ref=harv (help)
• Marsden, Colin J. (1983). Motive Power Combined Volume. Ian Allan. ISBN 0711012849. {{cite book}}: Invalid |ref=harv (help)
• Marsden, Colin J. (2011). Traction Recognition (2nd ed.). Ian Allan. ISBN 9780711034945. {{cite book}}: Invalid |ref=harv (help)

External links

• The Railcar Association on Class 121s