They ran their first trials between Didcot and Newbury (DN&S) during w/c 28 Apr 1952.
As a demonstration train it was naturally trialed around many parts of the country. The first demonstration was to Gerrards Cross, on the 23rd May, and then based on Neasden shed it worked a series of trials out of Marylebone on outer London suburban routes. Initially this was on the High Wycombe / Princes Risborough line, working 2 trains each way daily.
The first image, although taken at Marylebone, was a ScR publicity photo - captioned "Photograph shows A.C.V. lightweight diesel train arriving at Marylebone Station. The train is shortly going into experimental service." A.A. McLean Collection
From June 16th to June 27th 1952 the cars worked Mondays to Fridays as part of the shuttle service over the then steam worked, Epping to Ongar branch.
On the 19th July 1952 it was working the St Albans - Watford Junction line, during a 2-week stint. It was reported to be worked as 1, 2 and 3 cars at different times.
The London Transport Metropolitan Line shuttle, from Chalfont & Latimer to Chesham, was worked by the set from October 13th to 24th '52. During the first week all three cars remained coupled together, but in the second week, in which the off peak service only was worked, a single car did the honours, with the other two cars stabled at Chesham.
The second image was taken during trials on the Scottish Region, the set is seen awaiting departure from Dalmellington on the 20th June 1953, with the 5.40pm to Ayr. Hamish Stevenson Collection.
In 1953 the set was tried on the Hull - S Howden (ex-H&B) service. This has previously been the preserve of the LNER Sentinel steam railcars (modern for their time), until withdrawal of those cars brought about regular usage of auto-trains.
Twelve days of demonstration runs in the Birmingham area were extended an extra fortnight until 12th September 1953. At this time it was thought that the the BTC would purchase the unit, and after fitting it with heaters for use during the winter months it would go into regular service either on the Southminster Branch (ER) or the Watford – St Albans line (LMR).
In late 1953 they were on trial for a short while on the Southern Region Allhallows-on-Sea branch in Kent, after which they moved back to the London Midland Region. The Wellingborough to Higham Ferrers branch was another route the unit was tested on.
The set had a week on the Belmont Branch 1st to 6th September 1954.
It also apparently worked from Hull on the H&B for a while, before the last remnants of that service succumbed.
It made it's third appearance on the Stanmore Branch on 18th October 1954. Between its previous visits in June and September, it was reported on the Wellingborough – Higham Ferres service in July and on the Foxfield – Consiton branch early in August, noted there on the 19th where running was good and schedules were improved on throughout.
Around Oct. ’54 it was announced that a diesel service would begin between Watford Junction and St. Albans that winter, although this was considerably delayed whilst modifications were done to 79743-7.
M79740-2 re-appeared on the Harrow – Belmont service on the 25/4/55.
The vehicles eventually replaced steam on the Watford - St Albans branch on the 25th July 1955. The 3-car set moving from the Harrow - Belmont service, and for the move it was repainted into green with cream lining. It performed the 6½ mile journey in 15 mins, compared with 17 mins by steam. There were three more trains a day Monday - Friday inclusive, 11 more on Saturdays and 8 on Sundays. It is understood that the makers are to supply an additional 3-car set, and a motor car and trailer as spares.
With the delivery of the final 3-car set to Watford, diesel operation of the Harrow - Belmont branch was resumed in August Bank Holiday week 1957.
Introduced to Watford – St. Albans services on 25/7/55, during one month in ’56 they carried 35,095 passengers, for the same month in ’57 they carried 37,877, an increase of 2,782.
On 1/11/57 the Watford - St Albans line was noted as being worked by two 3-car sets, 79740/7/2 and 79744/6/3.
By April 1958 the Belmont branch was steam worked, as the serviceable ACV cars were confined to the St. Albans line, after only a brief appearance between Harrow and Belmont. They did return soon after, although not without trouble. The Belmont service was cancelled on the evening of 22/7/58 and steam locos took over for the next three days, the vehicle returning on the Saturday. The following month the DMU set on the St Albans branch was under repair, and so the only serviceable ACV set 79740/3/6 had to cover this from the 11th to 13th Aug, with steam once again on the Belmont branch. Two cars, believed to be 79744/9, had recently been badly damaged in a shunting accident at Watford.
A traffic census was taken on the Harrow-Belmont line on the w/e 17/10/58. Several trips daily during the peak hour carried over 100 passengers. An innovation on the 18th Oct. was the use of 79743 singly, and this arrangement continued for the rest of the month. A Derby Lightweight twin worked the line on the evening of 11/11/58. The ACV set was back in action the following morning, but by the evening, the line was in the hands of a Derby Lightweight twin, which continued on it for some time. The passengers welcomed the change, it only had a lack of doors for passengers use against it. The ACV vehicles apparently went into departmental use at this time, at Watford.
In February 1959 they were all officially placed in store at 1C.
In April '59 it was noted that the vehicles were still being used “in cases of extreme emergency”. Apparently an emergency had occurred every Sunday since mid-Nov ’58, as they were regularly used on the St. Albans branch whilst the Park Royal sets operated a shuttle service between Wembley and Harrow, during track work on the electric line between North Wembley and Wembley. The St. Albans branch was normally run by a single vehicle, such as 79743 on 22/3/59, but on the 12th April a 3-car set 79742/5/6 was working. On the 24th March 50413 failed before leaving the shed for the Belmont line, and 79742/5 were rustled up, without a trailer.
They continued to be used between Harrow and Belmont. Failures of the vehicles saw morning services on this line Belmont worked by steam on the mornings of the 17th/18th June, and the evening of the 10th July 1959.
Late in 1959 trouble with cracked bogie frames on the Park Royal Class 103s caused an acute shortage of DMUs, meaning the ACVs reappeared on the St. Albans and Belmont branches. When these vehicles failed services had to be cancelled, as Watford’s stored auto-fitted engines had departed by mid-Dec ’59. No passenger service ran between Harrow and Belmont after the morning service on 23/12/59 because of this, until the morning of the 29th when a Park Royal set returned. The service was again suspended on the afternoon of the 6th and the morning of the 7th, by which a steam train was provided. Steam continued to work the services with borrowed engines, with 79742/3/5 on standby for boiler washouts etc.
With the exception of 21/1/60 (no service) and 22/1/60 (steam loco / auto coach), 79742/5/7 worked the Belmont branch continuously from the middle of Jan until it failed on Saturday 12/2/60. The services were then taken over that day by a Class 103.
The three vehicles latterly used on the Harrow – Belmont service 79742/5/7 didn't reach Derby Friargate till about September 1961, and went behind the goods shed at the end of a siding. The other ACV cars were located over half-a-mile to the west of Friargate station, having arrived mid-'60.
They remained in storage at Derby for several years before entering the C&W works for disposal at the end of 1963. None survive.