The Class 121, like the
Class 122, was a single-car diesel multiple unit - though unpowered trailers (originally known as
Class 149) with cabs at one end were also built to supplement capacity during times of peak demand [1]. The Class 121, which was nicknamed the Bubble Car, was the last survivor of the first generation of British Railway DMU and remained in service until 2017.
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| Sandite unit 960 014 at Aylesbury |
| Information |
| Number built: |
26 cars (16 DMBS 10 trailers) |
| Built: |
1960 |
| Builder: |
Pressed Steel |
| Engine: |
2 AEC or Leyland 1595 diesels per DMBS |
| Power: |
300 hp (220 kW) |
| Formation: |
Driving Motor Brake Standard (DMBS)+[Driving Trailer Standard (DTS)] |
The Class 121s were allocated to British Rail's Western Region working on lightly used branch lines in Cornwall and along the Thames Valley. Originally in BR green they later carried BR blue and grey and some also received Network South East livery [2]. In the privatisation era they have worked with Silverlink and Arriva Trains Wales as well as their final operator Chiltern Railways.
The Class 121 outlasted all other first generation DMUs, a small number remained in service until 2017 on the
Princes Risborough -
Aylesbury branch line having been fitted with central door locking to meet current safety standards [3]. When finally withdrawn they were the last remaining first generation British Railways DMU in service, and also the last surviving vacuum braked passenger stock.
A number of Class 121s also found a new role in departmental service and were renumbered in the
Class 960 sequence. They have been used for route learning, track surveying and sandite depositing. Thirteen DMBS and two trailers have been preserved.
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| Chiltern 121 020 at Aylesbury |
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| Side view of preserved W55023 at Chinnor |
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| W55023 at Chinnor |
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| Preserved 960 010 at Chinnor |
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| Another view of W55023 |
[1] Brian Haresnape, Diesel Multiple Units, the First Generation (Ian Allan, 1985) p. 60
[2] Gavin Morrison, British Railway DMUs in Colour (Ian Allan, 2010) p. 33
[3] Colin J Marsden, DMU and EMU Recognition Guide (Ian Allan, 2013) p. 80
