Trial running of the first push-pull set started in mid-February 1972. Initially the formation consisted of six vehicles: 6101(ex-2646), 6304 (2621), 6301 (2647), 6302 (2605), 6303 (2645), 6201 (2606) and trials were conducted on the Cork line, the train being based in Inchicore. The first operations on the suburban section too place on 12 June 1972 when the train operated to Bray and Howth. For the next series of trials, which included a run to Enfield and back the formation was reduced to four cars.
The first revenue earning trip took place on 15 December 1972 with the train being formed by 6101, 6302, 6304, 6201. A second set: 6102 (ex-2626), 6301, 6303, 6202 (2632) operated a trial train to Drogheda on 20 December, while a third set: 6103 (ex-2618), 6305 (2663), 6307 (2665), 6204 (2610) was at that time in preparation in Inchicore Works.
At the end of 1972 / early 1973 there were 35 operational railcars - 31 AEC and 4 BUT. Railcar operation continued until 20 September 1975 when the last cars were placed in storage at Bray. The 21 October 1974 crash at Gormanston involved three trains: the 07:00 empty railcar from Connolly to Skerries (2651, 1356, 1414, 2642), the 07:00 empty push-pull from Pearse to Howth Junction (6102, 6305, 6307, 6204 propelled by B202) and the 06:50 Dundalk to Bray (B219 with 3 vans and 6 coaches).