The units took over services originally monopolised by GWR built railcars but as more and more cross country and branch lines closed that work became less and less. Consequently, the class was concentrated around the Reading, Bristol, Cardiff and Plymouth areas. They were used on the West London branch lines, the Severn Beach branch, lines in the Welsh valleys and the Cornish branch lines.
For the first 25 years of service the units were concentrated solely on the Western Region.
Eric Stuart notes: "at one time one use was to add on to Cross-Country units working the Newport - Shrewsbury - Crewe line. They were used to boost the available power. I recall that they were locked and had signs on the windows stating that they could only be used if specifically authorised by the Guard (presumably if the main unit was packed). One could see trains of 2 x CC units, each with its 121 - the CCs in blue and grey and the 121 in blue!"
W55034 on the Bridport branch, working the 10:35 from Maiden Newton in April 1975. Robert Frise Collection
In 1986 three, nos. 55032, 33 & 34 were transferred to Tyseley, now under Midland Region control, and used on local services around Birmingham.
The next three images by Mike Cooper were taken at Paddington in January 1988. First, two 121s added to a 3-car 101, and then two 121s added to a 3-car high density set. Finally a trio of 121s with a 2-car 101.
By 1992 only one example, no. 55026 was stationed at Plymouth Laira. Nos. 55032, 33 & 34 were at Tyseley and the remainder at Old Oak Common. The Old Oak Common fleet were used turn and turn about with the allocation of Class 117 driving cars as well as singly on the West London Branches.
Upon privatisation in 1997, only four vehicles remained in passenger service (55023/27/29/31) with Silverlink based at Bletchley. Used mainly on the Marston Vale Bletchley - Bedford line, they could also be found on other routes such as Gospel Oak - Barking. In 1996 55023 was withdrawn and the remaining three moved to the Sudbury branch on hire to Great Eastern. They were replaced by Class 150s in 2001.
55020 was resurrected from a sandite car for a return to passenger use for Chiltern Railways. It began operating the Aylesbury to Princes Risborough shuttle from 2003.
55032 had been in preservation at Crewe until bought by Arriva Trains Wales in 2005 for use on the Cardiff Bay branch. It was extensivly overhauled at LNWR's Crewe depot before being hauled south in June 2006. After some driver training on the Barry Tourist Railway it entered traffic on August 16th. It was withdrawn just three days later with engine troubles. It returning to service on the 14th September but reliability remained an issue thoughout its revival. It was sold to Chiltern Railways in March 2013, who put it into storage at Aylesbury, and it was again sold back to preservation in 2015.
55034 was another vehicle once preserved that returned to mainline passenger use. Following Chiltern's success with 55020, they added this vehicle to work with 55020 from May 2011. It carried BR green with yellow panel, the image show it arriving into Princes Risborough empty stock from Aylesbury on April 19, 2016, in readiness for two return trips from Princes Risborough, the first departing at 17.00. Stephen Burdett
The Winter 2016/2017 Chiltern Bubble Car Diagram was as follows:
06:35 Aylesbury (AYS)-Princes Risborough (PRR)
16:19 AYS-PRR Empty Coaching Stock
The Aylesbury - Princes Risborough shuttle ended in 2017, marking the end of first generation DMU use in passenger use on the network.