The first two sets were delivered in September 1958 to Bristol, being formed as power twins. Captions of images showing two-car sets in the green era often mention that the set is "running with the centre car removed", yet as there were three centre cars less than the matching power cars, two-car sets could be expected. Whether two-cars sets were deliberatly ordered for certain routes, or whether additional power cars were ordered to allow for maintenance, is unknown.
Overall fifteen sets would be delivered new to Bristol (including the three two-cars), nine to Cardiff, three to Tyseley (then a WR depot), and one to Reading. The last set was delivered in January 1960.
Their use was widespread throughout the Western Region and on services into the Midlands. The sets appear to have been associated with the Bristol-Weymouth workings from their introduction. There are photographs of a set on the Bromyard branch and on the Cambrian coast line.
Shortly after their introduction, sets were transferred from Cardiff to Reading to work the outer suburban services to Oxford. These were as seven-car sets, with the addition of Hawksworth composites adapted to run as DMU trailers. The image shows a seven-car set at Reading, date unknown. Adrian Vaughan.
As many Western Region lines closed, notable early use being the last passenger train over the Plympton branch. The Minehead, Calne and Bridport branches that have also since closed were also served by the sets.
The shrinkage of the system and the reduced need for sets, particularly two-cars, led to two sets of power cars (51053/61 and 51081/89) being transferred to Inverness depot in May 1968. They were never noted in traffic there, they sat outside the depot out of use, and were withdrawn in December that year. Afterwards, they remained for some time in the carrige sidings where they were used for spare parts for the depot's Class 120s. They were in plain blue livery with full yellow ends. In April 1970 W51061 was noted being being hauled from Corkerhill to Ayr for further stripping of spares and then back to Corkerhill via Cowlairs. It still carried its Reading set number 500 stencilled on both ends. Disposal for the four vehicles was by T.J. Thomson (Stockton) in September 1970. There would be no more withdrawals until 1985, demonstrating that this was one of the most successful DMU types.
The image shows set P588 at Exeter St. Davids in April 1975 with 51107 closest. As the set number prefix shows, by this date Plymouth Laira had some sets allocated to it. Robert Frise Collection.
By the end of 1982 almost all the vehicles were allocated to Reading depot. One of the main services they operated from here was onto the SR with a Reading-Gatwick Airport link, and the former SR line to Guildford / Redhill and Tonbridge. This appears to the first time that SR drivers would handle diesel-mechanical units in regular use, and they seem to have appreciated the larger cab windows than their own units (knicknaming them 'Glasshouses'), but found them very different to drive, particularly in challenging weather conditions.
Other Sets visited Skegness from Tyseley and provided the last conventional DMU service to the resort.
A book on the Central Wales line also suggests that one set was used while the line was severed at Glanrhyd. Stock redundant from Reading went to Tyseley for further service in the Midlands, from there they would operate routes such as to Skegness. A redundant set from Cardiff went to the North East in 1987 to help out during Pacer difficulties, which saw the Class reach places such as Whitby.
The last set to survive - 51073 and 51104 - were noted in Rail magazine on a driver training diagram that took it via Peterborough to Norwich in 1995. Afterwards they were sent to Penzance (they are pictured in the depot on 4th August 1995, Ian Buck) with the intention of covering the service to St Ives. Unfortunately too much work was required to make them servicable and they were withdrawn in June 1995, marking the end of the Class.