page_title: British Rail Class 121
section_title: Chiltern Railways
hierarchical_section_title: British Rail Class 121 / Past operations / Chiltern Railways
caption_attribution_description: English: British Rail class 121 "Bubble Car" no. 121020, at Bewdley on the Severn Valley Railway, whilst taking part in the Railcar 50 event. This unit is the last heritage unit operated in normal traffic, and is used on Chiltern Railways' Aylesbury to Princes Risborough shuttle services.
context_page_description: 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. 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.
  The Class 121 is Britain's longest serving DMU, operating in passenger service for 57 years until 2017.
context_section_description: 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  Chiltern's two final units were withdrawn from service on 19 May 2017, due to difficulties in obtaining spare parts, and will be sold.
caption: 121020 and 121034 at Bewdley in 2004.
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