British Rail Class 121

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.
== Details ==
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.
== Privatisation ==
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.
=== 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 SouthEastlivery. 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 ===
In 2003, Chiltern Railways reintroduced "Heritage" diesel multiple units on its Aylesbury to Princes Risboroughshuttle 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, becoming the final first generation multiple units in service in the UK.
== Fleet details ==
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 DMBS unit to be withdrawn and scrapped. In 2011, numbers, 55021 (960021) and 55030 (960013) were also scrapped.
Class 	Operator 	No. in Service	Year Built	Cars per Set	Unit nos.	Notes
Class 960	Network Rail	1 	1960 	1 	121022 	Reclassified as Class 960
== Preservation ==
Thanks to their extended usage in departmental service, the 121s have proven to be popular for preservation on heritage railways, with most of the class being preserved.
Vehicle no.	Vehicle no. 	Unit no.	Vehicle type	Location 	Notes
Original 	Departmental	Unit no.	Vehicle type	Location 	Notes
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 	Chinnor and Princes Risborough Railway 	Returned 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 Tunnelemergency 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, awaiting preservation
== 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 	
== Gallery ==
File:Unit 55028 Set No L128.JPEG
File:Jpg 1612696541-359.jpg
File:W55033 at Colne Valley Railway 2.JPG
File:121020 at Bewdley.JPG
Category:Diesel trainsets
Category:United Kingdom
Category:British Rail locomotives
Category:Diesel locomotives
Category:Built in 1960
Category:British Rail diesel locomotives