British Rail Class 121

British Rail Class 121
Class 121 in Network South East livery at Paddington station – note the exhaust pipes and plated-over headcode box (1988)
In service	1960–present
Manufacturer	Pressed Steel Company
Number built	16 motor cars 10 trailer cars
Number preserved	5 motor, 2 trailer
Formation	Single car
Fleet numbers	55020–55035
Operator(s)	Chiltern Railways Network Rail
Line(s) served	Princes Risborough to Aylesbury Line
Specifications
Car body construction	Steel
Car length	64 ft 6 in (19,660 mm)
Width	9 ft 3 in (2,820 mm)
Height	12 ft 4 in (3,760 mm)
Weight	DMBS: 37 long tons 8 cwt (83,800 lb or 38 t) DTS: 29 long tons 7 cwt (65,700 lb or 29.8 t)
Coupling system	Screw
Multiple working	■ Blue Square
Track gauge	4 ft 8 1⁄2 in (1,435 mm)

Sixteen Class 121 single-car, double-ended 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 now endorsed by current operator Chiltern Railways).

The Class 121 is Britain's longest serving DMU, having been in service for 55 years as of 2015.

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.

Class 121s were built with distinctive exhaust pipes, designed to fit around a large four-digit route headcode indicator box at roof level. Use of the headcode indicator box was discontinued in the 1970s, so the indicator was removed and the hole plated-up when the units were refurbished.

They also had a small destination indicator inside the top of the centre cab window.

The similar Class 122 units had the small destination indicator in the cab roof in place of the large headcode box. They were used on the other regions of British Rail.

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. There are three examples left in revenue-making service.

Chiltern Railways

In 2003, Chiltern Railways reintroduced "Heritage" diesel multiple units on its Aylesbury to Princes Risborough shuttle service. For this purpose, unit 121 020 (vehicle 55020) 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 the 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 121 034, 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 is also used on Aylesbury to Princes Risborough services, when required.

Both units are 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 121 032 from Arriva Trains Wales, which was sold on in 2015, for preservation.

Network Rail

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 jointly used by Chiltern Railways for route learning.

Current fleet

The current fleet is listed below:

Unit no.	Vehicle no.		Livery	Use	Status
	Current no.	Previous no.
121 020	55020	977722	Chiltern Railways blue	-	In traffic (based at Chiltern Railways Aylesbury depot) following departmental use as 960 002
960 014	977873	55022	BR Blue/Grey	Route-learning unit	In traffic (based at Chiltern Railways Aylesbury depot)
121 034	55034	-	British Railways coaching stock green	-	In traffic (based at Chiltern Railways Aylesbury depot), from preservation at Tyseley Locomotive Works, as 121 034

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 Gospel Oak to Barking. 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 (121 027/029) were repainted into Silverlink's purple and green livery, and the third (121 031) was repainted into Network SouthEast livery. The three units also received names from withdrawn Class 117 units.

• 121 027 - Bletchley TMD
• 121 029 - Marston Vale
• 121 031 - Leslie Crabbe

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

Arriva Trains Wales

In 2006, unit 121 032 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, 121 032 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.

Preservation

"Bubble Cars" have proved popular for preservation on heritage railways. Including some in the class still in Service.

Vehicle no.		Unit no.	Vehicle type	Location	Comments
Original no.	Departmental no.
56287	-	L211	DTS	Colne Valley Railway	-
56289	-	L263	DTS	East Lancashire Railway	-
55023	-	L123	DMBS	Chinnor & Princes Risborough Railway	Repainted into BR Green livery whilst based at Bletchley depot.
55024	977858	L124	DMBS	Chinnor & Princes Risborough Railway	Repainted into BR Coaching Stock maroon livery while based at Aylesbury depot. Awaiting restoration.
55027	977975	P127	DMBS	Ecclesbourne Valley Railway	Previously Severn Tunnel Emergency train 960 302, sold to Barry Tourist Railway around January 2014 and then on to the Ecclesbourne Valley Railway in June 2014.
55028	977860	L128	DMBS	Swanage Railway	Recently sold by South West Trains, it was used as a departmental route-learning unit. Currently in B.R "Heritage" green with "D.M.U Whiskers" livery after a major overhaul was undertaken after its arrival. Currently at Eastleigh under overhaul to allow eventual use on the mainline connection to Wareham.
55029	977968	L129	DMBS	Rushden, Higham and Wellingborough Railway	Recently sold by Colas Rail from store at Rugby. It was converted there into non-passenger carrying stock. Damaged in fire, May 2015.
55031	977976	T002	DMBS	Ecclesbourne Valley Railway	Previously Severn Tunnel Emergency train 960 303, sold to Barry Tourist Railway around January 2014 and then on to the Ecclesbourne Valley Railway in June 2014.
55032		T003	DMBS	Wensleydale Railway	In Arriva Trains Wales livery, stored
55033	977826	T004	DMBS	Colne Valley Railway	Painted in experimental MidLine livery. It's currently in B.R "Heritage" green with "D.M.U Whiskers" livery.
55034	977828	T005	DMBS	Chiltern Railways	Initially preserved at Birmingham Railway Museum. Returned to capital stock with Chiltern Railways as 121 034.

Fleet 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

Present fleet

Class	Operator	No. in Service	Year Built	Cars per Set	Unit nos.	Notes
Class 121	Chiltern Railways	2	1960	1	121 020, 121 034
	Network Rail	1			121 022	Reclassified as Class 960

Remarkably, considering the age of the fleet, the oldest unit (55020) is still in daily service, whilst the youngest vehicle (55035) was the first to be dismantled. As at July 2014 55021 (960 021) and 55030 (960 013) have also been scrapped.

External links

• The Railcar Association on Class 121s