British Rail Class 121
Class of British diesel multiple units
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The British Rail Class 121 diesel multiple units were built by Pressed Steel from 1960 to 1961. Sixteen driving motor vehicles were built, numbered 55020–55035, which 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.
- 30518 (DMBS)
- 30519 (DTS)[2]
| British Rail Class 121 Bubble Car | |
|---|---|
A Class 121 at Reading in 1992 | |
 Interior of 121032 | |
| In service | May 1960 – present |
| Manufacturer | Pressed Steel Company[1] |
| Order no. |
|
| Family name | First generation |
| Replaced | Steam locomotives and carriages GWR railcars |
| Constructed | 1960–1961 |
| Entered service | 1960 |
| Scrapped | 1978–2011 |
| Number built |
|
| Number preserved |
|
| Number scrapped |
|
| Formation |
|
| Diagram | |
| Fleet numbers |
|
| Capacity |
|
| Operators | British Railways, Network SouthEast, Regional Railways, Silverlink, Railtrack, Network Rail, Arriva Trains Wales, Chiltern Railways |
| Depots | |
| Lines served | |
| Specifications | |
| Car body construction | Steel[1] |
| Car length | 64 ft 6 in (19,660 mm) (over body)[4] |
| Width | 9 ft 0 in (2,740 mm) (over body)[4] |
| Height | 12 ft 4+1⁄2 in (3,772 mm)[4] |
| Doors | Slam[1] |
| Articulated sections | Single car (2) |
| Wheelbase |
|
| Maximum speed | 70 mph (113 km/h)[4] |
| Weight |
|
| Prime mover(s) | |
| Engine type | 11.1-litre naturally aspirated Diesel |
| Cylinder count | 6 (horizontal) per engine [4] |
| Power output | 300 hp (220 kW) (DMBS)[1] |
| Transmission | Mechanical (DMBS)[4] |
| HVAC | Oil burning air heater[4] |
| Bogies |
|
| Braking system(s) | Vacuum[4] |
| Safety system(s) | AWS (DMBS)[4] |
| Coupling system | Screw[11] |
| Multiple working | ■ Blue Square[1] |
| Headlight type | Fluorescent and tungsten[4] |
| Track gauge | 4 ft 8+1⁄2 in (1,435 mm) |
British Railways service
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 in 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, the Class 121 had a four-character headcode box in the roof dome, with the destination indicator inside the top of the centre cab window.
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. 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) into Network SouthEast livery. The three units also received names from withdrawn Class 117 units.
- 121027 - Bletchley TMD[14]
- 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.
Chiltern Railways
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 165032 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.[15]
Both units were additionally used on shuttles, as required, between Aylesbury and Quainton Road, 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.[16]
Current operations
Upon the privatisation of British Rail, the Class 121 fleet was only operated by one train operating 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.
As of 2026, two units are owned by Locomotive Services Limited:
- 55022 (former Chiltern Railways/Network Rail route learner 977873/960014) was acquired in 2016.[17] It has been heavily refurbished and, as of September 2023, operates as part of the chairman's private fleet, bearing the name 'Flora'.[18]
- 55034 (former Chiltern Railways 121034) was acquired for use as a route learner in 2017.[19] It has since been loaned to heritage railways; as of June 2024, it is on loan to the Cholsey and Wallingford Railway, having previously been loaned to the Ecclesbourne Valley Railway.[20]
Preservation
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[21] | |
| 56289 | – | L263 | DTS | East Lancashire Railway | |
| 55020 | 977722 | L120 | DMBS | Bodmin and Wenford Railway[22] | Departmental unit 960002 (1992–2002) then returned to passenger use until 2017[23] |
| 55023 | – | L123 | DMBS | Chinnor and Princes Risborough Railway | |
| 55024 | 977858 | L124 | DMBS | Returned to traffic 30 March 2019 | |
| 55025 | 977859 | L125 | DMBS | Vale of Berkeley Railway | Unit sorted pending restoration[24] |
| 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.[25] |
| 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. |
Order details
| 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
An OO gauge model of the Class 121 was produced by Lima in 1998, as unit 55035 in all-over rail blue livery and unit 55027 in Network SouthEast livery.[26] In 2006, Hornby Railways launched its first version of the BR Class 121 in OO gauge.[27] This model was produced in BR blue and BR green, using the Lima body mouldings that Hornby had acquired.[28] Since 2017, Hornby have produced a basic representation of the prototype as part of their Railroad range in BR Green.
